net: Make setsockopt() optlen be unsigned.

This provides safety against negative optlen at the type
level instead of depending upon (sometimes non-trivial)
checks against this sprinkled all over the the place, in
each and every implementation.

Based upon work done by Arjan van de Ven and feedback
from Linus Torvalds.

Signed-off-by: David S. Miller <davem@davemloft.net>

net/socket.c

@@ -2391,7 +2391,7 @@ int kernel_getsockopt(struct socket *sock, int level, int optname,
 }
 
 int kernel_setsockopt(struct socket *sock, int level, int optname,
-			char *optval, int optlen)
+			char *optval, unsigned int optlen)
 {
 	mm_segment_t oldfs = get_fs();
 	int err;