Allow specifying 'to' address without having an etho interface.

1) For Deny and Reject, I think it is dangerous to default to denying/rejecting packets only to the eth0 IP address. If I have two interfaces, and do ufw::deny { 'foo': port => x, proto => 'tcp' }, wouldn't I expect the deny rule to apply to both my interfaces?

2) For allow, maybe $::ipaddress alone would be a sensible default? I tried to maintain backwards compatibility while still fixing the bug that prevented my specified $ip from being used, since my $ipaddress_eth0 == undef.