Ensure the match happens in the right direction, previously the
destination used was the server, not the NAT host, as the comment
shows the code intended.
Additionally nf_nat_irc uses port 0 as a signal and there's no valid way
it can appear in a DCC message, so consider port 0 also forged.
Fixes: 869f37d8e48f ("[NETFILTER]: nf_conntrack/nf_nat: add IRC helper port") Signed-off-by: David Leadbeater <dgl@dgl.cx> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>