ipfilter: Print protocol when listing NAT table mappings

NAT table mappings list only the source and destination IP, the source
and destinaion port numbers, and their mappings. But the protocol is not
listed. Now that Facebook and Google use QUIC, seeing port 443 in in a
list of active NAT sessions could mean 443/tcp or 443/udp. This patch
adds the protocol to the listing to aid in determining whether HTTPS is
TCP or QUIC in a NAT mapping listing. This also helps differentiatinete
between other protocols such as ICMP, ESP, and AH in ipnat list of active
sessions.

MFC after: 1 week