sctp: remove the out_nounlock label in sctp_setsockopt

This is just used once, and a direct return for the redirect to the AF
case is much easier to follow than jumping to the end of a very long
function.

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