Use `NFPROTO_*` constants for protocol families

Use `NFPROTO_*` constants for protocol families

Netfilter has a set of `NFPROTO_*` constants for the protocol families that it
supports, in part because it supports protocols and pseudo-protocols that do not
have `PF_*` (and `AF_*`) constants.  Currently, ulogd uses `AF_*` constants for
protocol families, because it does not support any families which do not have
`AF_*` constants.  Switch to `NFPROTO_*` constants instead, so we can add ARP
support later.

In the IP2* filters, retain `AF_*` for address family variables.

Remove a stray semicolon.

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Florian Westphal <fw@strlen.de>