hostnet: if TCP is sent to us, don't forward it randomly elsewhere
hostnet: if TCP is sent to us, don't forward it randomly elsewhere

If the peer initiates a TCP connection to us (rather than through us
as a gateway) then forward the connection on to a real IP of ours
(127.0.0.1) rather than connect to some other random host on the internet.

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

djs55/vpnkit,djs55/vpnkit,samoht/vpnkit,djs55/vpnkit