[NETFILTER] ebtables: Support nf_log API from ebt_log and ebt_ulog

This makes ebt_log and ebt_ulog use the new nf_log api.  This enables
the bridging packet filter to log packets e.g. via nfnetlink_log.

Signed-off-by: Bart De Schuymer <bdschuym@pandora.be>
Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>