[NETFILTER]: nfnetlink_log: fix reference leak

Stop reference leaking in nfulnl_log_packet(). If we start a timer we
are already taking another reference.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Adrian Bunk <bunk@stusta.de>