if we have ipv4NativeRoutingCIDR: 0.0.0.0/0 configured though helm,
agent may have following complain

level=error msg="iptables rules full reconciliation failed, will retry
another one later" error="failed to install rules: cannot install
masquerade rules: unable to run 'iptables -t nat -A CILIUM_POST_nat ! -d
0.0.0.0/0 -s 10.0.2.0/24 ! -o cilium_+ -m comment --comment cilium
masquerade non-cluster -j MASQUERADE' iptables command: exit status 4
stderr=\"iptables v1.8.8 (nf_tables):  RULE_APPEND failed (Invalid
argument): rule in chain CILIUM_POST_nat\\n\"" subsys=iptables

That's because nf_tables doesn't allow 0.0.0.0/0 but iptable legacy and
our bpf masquerade can support it.

Here is the test from my laptop

root@kind-worker3:/# iptables -t nat -A POSTROUTING ! -d 0.0.0.0/0 -o
eth0 -j MASQUERADE
iptables v1.8.9 (nf_tables):  RULE_APPEND failed (Invalid argument):
rule in chain POSTROUTING
root@kind-worker3:/# iptables-legacy -t nat -A POSTROUTING ! -d
0.0.0.0/0 -o eth0 -j MASQUERADE
root@kind-worker3:/# iptables-legacy-save
*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [10:592]
:POSTROUTING ACCEPT [10:592]
-A POSTROUTING ! -d 0.0.0.0/0 -o eth0 -j MASQUERADE

This PR will detect the iptable mode and tell users to use
enable-ipv4-masquerade or enable-ipv6-masquerade: false in nft mode

Signed-off-by: Liyi Huang <liyi.huang@isovalent.com>