netfilter: nf_log: add packet logging for netdev family

Move layer 2 packet logging into nf_log_l2packet() that resides in
nf_log_common.c, so this can be shared by both bridge and netdev
families.

This patch adds the boiler plate code to register the netdev logging
family.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_log.h

@@ -109,5 +109,10 @@ void nf_log_dump_packet_common(struct nf_log_buf *m, u_int8_t pf,
 			       const struct net_device *out,
 			       const struct nf_loginfo *loginfo,
 			       const char *prefix);
+void nf_log_l2packet(struct net *net, u_int8_t pf, unsigned int hooknum,
+		     const struct sk_buff *skb,
+		     const struct net_device *in,
+		     const struct net_device *out,
+		     const struct nf_loginfo *loginfo, const char *prefix);
 
 #endif /* _NF_LOG_H */