net/smc: fix error return code in smc_setsockopt()

Fix to return error code -EINVAL instead of 0 if optlen is invalid.

Fixes: 01d2f7e2 ("net/smc: sockopts TCP_NODELAY and TCP_CORK")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>