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 <[email protected]>

net/ax25/af_ax25.c

@@ -534,7 +534,7 @@ ax25_cb *ax25_create_cb(void)
  */
 
 static int ax25_setsockopt(struct socket *sock, int level, int optname,
-	char __user *optval, int optlen)
+	char __user *optval, unsigned int optlen)
 {
 	struct sock *sk = sock->sk;
 	ax25_cb *ax25;