input: UNIXSOCK: prevent unaligned pointer access

input: UNIXSOCK: prevent unaligned pointer access

`struct ulogd_unixsock_packet_t` is packed, so taking the address of its
`struct iphdr payload` member may yield an unaligned pointer value.  We
only actually dereference the pointer to get the IP version, so replace
the pointer with a version variable and elsewhere use `pkt.payload`
directly.

Remove a couple of stray semicolons.

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>