net: socket: suppress unused warning

net: socket: suppress unused warning

suppress unused warnings and fix the error that there is
with the W=1 enabled.

Warning generated

net/socket.c: In function ‘__sys_getsockopt’:
net/socket.c:2300:13: error: variable ‘max_optlen’ set but not used [-Werror=unused-but-set-variable]
 2300 |         int max_optlen;

Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20230310221851.304657-1-vincenzopalazzodev@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>