tcp, udp: Don't precompute port remappings in epoll references

The epoll references for both TCP listening sockets and UDP sockets
includes a port number.  This gives the destination port that traffic
to that socket will be sent to on the other side.  That will usually
be the same as the socket's bound port, but might not if the -t, -u,
-T or -U options are given with different original and forwarded port
numbers.

As we move towards a more flexible forwarding model for passt, it's
going to become possible for that destination port to vary depending
on more things (for example the source or destination address).  So,
it will no longer make sense to have a fixed value for a listening
socket.

Change to simpler semantics where this field in the reference gives
the bound port of the socket.  We apply the translations to the
correct destination port later on, when we're actually forwarding.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

tcp_splice.c

@@ -420,10 +420,12 @@ static int tcp_splice_new(const struct ctx *c, struct tcp_splice_conn *conn,
 	int s = -1;
 
 	if (pif == PIF_SPLICE) {
+		port += c->tcp.fwd_out.delta[port];
 		s = tcp_conn_sock(c, af);
 	} else {
 		ASSERT(pif == PIF_HOST);
 
+		port += c->tcp.fwd_in.delta[port];
 		s = tcp_conn_sock_ns(c, af);
 	}