audit: normalize NETFILTER_PKT

Eliminate flipping in and out of message fields, dropping fields in the
process.

Sample raw message format IPv4 UDP:
type=NETFILTER_PKT msg=audit(1487874761.386:228):  mark=0xae8a2732 saddr=127.0.0.1 daddr=127.0.0.1 proto=17^]
Sample raw message format IPv6 ICMP6:
type=NETFILTER_PKT msg=audit(1487874761.381:227):  mark=0x223894b7 saddr=::1 daddr=::1 proto=58^]

Issue: https://github.com/linux-audit/audit-kernel/issues/11
Test case: https://github.com/linux-audit/audit-testsuite/issues/43



Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>