netfilter: nfnetlink_log: Change setter functions to be void

Change return type of nfulnl_set_timeout() and nfulnl_set_qthresh() to
be void.

This patch changes the return type of the static methods
nfulnl_set_timeout() and nfulnl_set_qthresh() to be void, as there is no
justification and no need for these methods to return int.

Signed-off-by: Rami Rosen <rami.rosen@intel.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>