test: check that one (src, src_port) creates one NAT rule
test: check that one (src, src_port) creates one NAT rule

This test creates 2 physical servers and sends traffic to them from
the same (src, src_port) and checks that both packets use the same
NAT rule i.e. the table size doesn't increase when the second
(dst, dst_port) is seen.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@docker.com>

djs55/vpnkit,djs55/vpnkit,djs55/vpnkit