[NETFILTER]: nfnetlink_queue: kill useless wrapper

nfqnl_set_mode takes the queue lock and calls __nfqnl_set_mode. Just move
the code from __nfqnl_set_mode to nfqnl_set_mode since there is no other
user.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>