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/atm/common.c

@@ -679,7 +679,7 @@ static int check_qos(const struct atm_qos *qos)
 }
 
 int vcc_setsockopt(struct socket *sock, int level, int optname,
-		   char __user *optval, int optlen)
+		   char __user *optval, unsigned int optlen)
 {
 	struct atm_vcc *vcc;
 	unsigned long value;