bpf: Clean up and generalize ipv4_to_ipv6/ipv6_to_ipv4 functions
bpf: Clean up and generalize ipv4_to_ipv6/ipv6_to_ipv4 functions

Early spring clean up on the old NAT46/64 handling code in order to make
it more generic. Allow to pass target source/destination addresses into
the two ipv4_to_ipv6() / ipv6_to_ipv4() helpers.

Signed-off-by: Daniel Borkmann <3d0f3b9ddcacec30c4008c5e030e6c13a478cb4f@iogearbox.net>

cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium