Previously, regenerating an endpoint manually via CLI resulted in
compilation errors as seen below. These errors occurred because the
endpoint headerfile (ep_config.h or lxc_config.h) was not written to the
`<endpoint ID>_next` directory (will be reffered to as "next"), where
the BPF compilation takes place.

The reason the headerfile was not written to the "next" directory was
because Cilium only wrote the headerfile if it was changed (via hash).
However, a manual regeneration triggered through the API, sets the
regeneration level to "compile+load" (a full regeneration), where Cilium
expects all relevant files, including the headerfile, to be present in
the "next" directory (`<endpoint ID>_next`). Hence, the compilation
errors.

This commit fixes this issue by checking whether there has been a
request for a full regeneration, in which case, we write the headerfile
to the "next" directory.

```
root@k8s2:/var/run/cilium/state# clang -emit-llvm -O2 -target bpf -std=gnu89 -nostdinc -D__NR_CPUS__=2 -Wall -Wextra -Werror -Wshadow -Wno-address-of-packed-member -Wno-unknown-warning-option -Wno-gnu-variable-s
ized-type-not-at-end -Wdeclaration-after-statement -I/var/run/cilium/state/globals -I1285_next -I/var/lib/cilium/bpf -I/var/lib/cilium/bpf/include -c /var/lib/cilium/bpf/bpf_lxc.c -o /tmp/c
In file included from /var/lib/cilium/bpf/bpf_lxc.c:22:
/var/lib/cilium/bpf/lib/icmp6.h:50:29: error: use of undeclared identifier 'NODE_MAC'
        union macaddr smac, dmac = NODE_MAC;
                                   ^
/var/lib/cilium/bpf/lib/icmp6.h:359:30: error: use of undeclared identifier 'NODE_MAC'
                union macaddr router_mac = NODE_MAC;
                                           ^
In file included from /var/lib/cilium/bpf/bpf_lxc.c:26:
/var/lib/cilium/bpf/lib/lxc.h:67:29: error: use of undeclared identifier 'NODE_MAC'
        union macaddr router_mac = NODE_MAC;
                                   ^
/var/lib/cilium/bpf/bpf_lxc.c:159:10: error: implicit declaration of function 'lookup_ip6_remote_endpoint' [-Werror,-Wimplicit-function-declaration]
                info = lookup_ip6_remote_endpoint(&orig_dip);
                       ^
/var/lib/cilium/bpf/bpf_lxc.c:159:10: note: did you mean 'lookup_ip6_endpoint'?
/var/lib/cilium/bpf/lib/eps.h:13:1: note: 'lookup_ip6_endpoint' declared here
lookup_ip6_endpoint(struct ipv6hdr *ip6)
^
/var/lib/cilium/bpf/bpf_lxc.c:159:8: error: incompatible integer to pointer conversion assigning to 'struct remote_endpoint_info *' from 'int' [-Werror,-Wint-conversion]
                info = lookup_ip6_remote_endpoint(&orig_dip);
                     ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/lib/cilium/bpf/bpf_lxc.c:529:10: error: implicit declaration of function 'lookup_ip4_remote_endpoint' [-Werror,-Wimplicit-function-declaration]
                info = lookup_ip4_remote_endpoint(orig_dip);
                       ^
/var/lib/cilium/bpf/bpf_lxc.c:529:10: note: did you mean 'lookup_ip4_endpoint'?
/var/lib/cilium/bpf/lib/eps.h:35:1: note: 'lookup_ip4_endpoint' declared here
lookup_ip4_endpoint(const struct iphdr *ip4)
^
/var/lib/cilium/bpf/bpf_lxc.c:529:8: error: incompatible integer to pointer conversion assigning to 'struct remote_endpoint_info *' from 'int' [-Werror,-Wint-conversion]
                info = lookup_ip4_remote_endpoint(orig_dip);
                     ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/lib/cilium/bpf/bpf_lxc.c:1027:10: error: implicit declaration of function 'lookup_ip6_remote_endpoint' [-Werror,-Wimplicit-function-declaration]
                info = lookup_ip6_remote_endpoint(src);
                       ^
/var/lib/cilium/bpf/bpf_lxc.c:1027:8: error: incompatible integer to pointer conversion assigning to 'struct remote_endpoint_info *' from 'int' [-Werror,-Wint-conversion]
                info = lookup_ip6_remote_endpoint(src);
                     ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/lib/cilium/bpf/bpf_lxc.c:1256:10: error: implicit declaration of function 'lookup_ip4_remote_endpoint' [-Werror,-Wimplicit-function-declaration]
                info = lookup_ip4_remote_endpoint(ip4->saddr);
                       ^
/var/lib/cilium/bpf/bpf_lxc.c:1256:8: error: incompatible integer to pointer conversion assigning to 'struct remote_endpoint_info *' from 'int' [-Werror,-Wint-conversion]
                info = lookup_ip4_remote_endpoint(ip4->saddr);
                     ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
11 errors generated.
```

Fixes cilium#10630
Fixes cilium#12005

Signed-off-by: Chris Tarazi <chris@isovalent.com>