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>
diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
index 5e6c072..7fa9c7a 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -409,7 +409,7 @@
  */
 
 static int x25_setsockopt(struct socket *sock, int level, int optname,
-			  char __user *optval, int optlen)
+			  char __user *optval, unsigned int optlen)
 {
 	int opt;
 	struct sock *sk = sock->sk;