net/bpfilter: split __bpfilter_process_sockopt

Split __bpfilter_process_sockopt into a low-level send request routine and
the actual setsockopt hook to split the init time ping from the actual
setsockopt processing.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>