…ersion_5.18.16

Feature #759: Upgrade autogen/libopts to 5.18.16

Sample output:

```
/Users/fklassen/git/tcpreplay/build/src/tcpreplay -i en0 -t pkt_too_long.pcap
Actual: 2 packets (196 bytes) sent in 0.000066 seconds
Rated: 2969696.9 Bps, 23.75 Mbps, 30303.03 pps
Flows: 2 flows, 30303.03 fps, 3 flow packets, 0 non-flow
Statistics for network device: en0
	Successful packets:        2
	Failed packets:            1
	Truncated packets:         0
	Retried packets (ENOBUFS): 0
	Retried packets (EAGAIN):  0
Warning in /Users/fklassen/git/tcpreplay/src/send_packets.c:send_packets() line 489:
Unable to send packet: Error with bpf send() [2]: Input/output error (errno = 5)

Process finished with exit code 0
```

Bug #751 don't exit after send error

Do not call exit without declaring it.  Add #include <unistd.h>
for fork.  Add missing int type to the definition of main.

Implicit ints and implicit function declarations were removed from
C in 1999 and will not be supported by future compilers.

…bustness

Bug #750: configure: libpcap version robustness

Flow, fps, flow packet counts make sense for many combinations of packet
modifiers and cache settings:

```
# tcpreplay -i enp0s5 -l1 --mbps=1 ping.pcap
Actual: 16 packets (1568 bytes) sent in 0.012564 seconds
Rated: 124801.0 Bps, 0.998 Mbps, 1273.47 pps
Flows: 2 flows, 159.18 fps, 16 unique flow packets, 0 unique non-flow packets
Statistics for network device: enp0s5
        Successful packets:        16
        Failed packets:            0
        Truncated packets:         0
        Retried packets (ENOBUFS): 0
        Retried packets (EAGAIN):  0

# tcpreplay -i enp0s5 -l1 --mbps=1 -K ping.pcap
File Cache is enabled
Actual: 16 packets (1568 bytes) sent in 0.012561 seconds
Rated: 124830.8 Bps, 0.998 Mbps, 1273.78 pps
Flows: 2 flows, 159.22 fps, 16 unique flow packets, 0 unique non-flow packets
Statistics for network device: enp0s5
        Successful packets:        16
        Failed packets:            0
        Truncated packets:         0
        Retried packets (ENOBUFS): 0
        Retried packets (EAGAIN):  0

# tcpreplay -i enp0s5 -l10 --mbps=1 ping.pcap
Actual: 160 packets (15680 bytes) sent in 0.125452 seconds
Rated: 124988.0 Bps, 0.999 Mbps, 1275.38 pps
Flows: 2 flows, 15.94 fps, 160 unique flow packets, 0 unique non-flow packets
Statistics for network device: enp0s5
        Successful packets:        160
        Failed packets:            0
        Truncated packets:         0
        Retried packets (ENOBUFS): 0
        Retried packets (EAGAIN):  0

# tcpreplay -i enp0s5 -l10 --mbps=1 -K ping.pcap
File Cache is enabled
Actual: 160 packets (15680 bytes) sent in 0.125451 seconds
Rated: 124989.0 Bps, 0.999 Mbps, 1275.39 pps
Flows: 2 flows, 15.94 fps, 16 unique flow packets, 0 unique non-flow packets
Statistics for network device: enp0s5
        Successful packets:        160
        Failed packets:            0
        Truncated packets:         0
        Retried packets (ENOBUFS): 0
        Retried packets (EAGAIN):  0

# tcpreplay -i enp0s5 -l10 --mbps=1 --unique-ip --unique-ip-loops=3 ping.pcap
Actual: 160 packets (15680 bytes) sent in 0.125451 seconds
Rated: 124989.0 Bps, 0.999 Mbps, 1275.39 pps
Flows: 20 flows, 159.42 fps, 160 unique flow packets, 0 unique non-flow packets
Statistics for network device: enp0s5
        Successful packets:        160
        Failed packets:            0
        Truncated packets:         0
        Retried packets (ENOBUFS): 0
        Retried packets (EAGAIN):  0

# tcpreplay -i enp0s5 -l10 --mbps=1 --unique-ip --unique-ip-loops=3 -K ping.pcap
File Cache is enabled
Actual: 160 packets (15680 bytes) sent in 0.125457 seconds
Rated: 124983.0 Bps, 0.999 Mbps, 1275.33 pps
Flows: 20 flows, 159.41 fps, 160 unique flow packets, 0 unique non-flow packets
Statistics for network device: enp0s5
        Successful packets:        160
        Failed packets:            0
        Truncated packets:         0
        Retried packets (ENOBUFS): 0
        Retried packets (EAGAIN):  0

# tcpreplay -i enp0s5 -l10 --mbps=1 --unique-ip --unique-ip-loops=3 ping.pcap
Actual: 160 packets (15680 bytes) sent in 0.125456 seconds
Rated: 124984.0 Bps, 0.999 Mbps, 1275.34 pps
Flows: 8 flows, 63.76 fps, 64 unique flow packets, 0 unique non-flow packets
Statistics for network device: enp0s5
        Successful packets:        160
        Failed packets:            0
        Truncated packets:         0
        Retried packets (ENOBUFS): 0
        Retried packets (EAGAIN):  0

# tcpreplay -i enp0s5 -l10 --mbps=1 --unique-ip --unique-ip-loops=3 -K ping.pcap
File Cache is enabled
Actual: 160 packets (15680 bytes) sent in 0.125450 seconds
Rated: 124990.0 Bps, 0.999 Mbps, 1275.40 pps
Flows: 8 flows, 63.77 fps, 64 unique flow packets, 0 unique non-flow packets
Statistics for network device: enp0s5
        Successful packets:        160
        Failed packets:            0
        Truncated packets:         0
        Retried packets (ENOBUFS): 0
        Retried packets (EAGAIN):  0

```

Bug #749 flow stats: avoid overstating flow packet count

Not only was the parsing wrong, but sometimes the wrong library was tested.

…dates

Bug #750 more libpcap version updates

e.g.

```
mkdir build
cd build
autoreconf --install --force --verbose .. 2>&1; ../configure --disable-local-libopts --with-testnic=enp0s5
make
sudo make test
```

Bug #767 tests: support for out-of-tree tests