Fix the SO_ZEROCOPY switch case on sock_setsockopt() avoiding the
ret values to be overwritten by the one set on the default case.

Fixes: 28190752 ("sock: permit SO_ZEROCOPY on PF_RDS socket")
Signed-off-by: NJesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
Acked-by: NWillem de Bruijn <willemb@google.com>
Acked-by: NSowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>