At this point optlen == sizeof(sfilter) but some compilers are dumb.

Reported-by: Németh Márton <nm127@freemail.h
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Acked-by: NOliver Hartkopp <oliver@hartkopp.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>