[NETFILTER]: nfnetlink_log: fix style

Fix function definition style to match other functions in nfnetlink_log.c.

Signed-off-by: Michal Miroslaw <mirq-linux@rere.qmqm.pl>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>