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/ipv4/ipmr.c

@@ -931,7 +931,7 @@ static void mrtsock_destruct(struct sock *sk)
  *	MOSPF/PIM router set up we can clean this up.
  */
 
-int ip_mroute_setsockopt(struct sock *sk, int optname, char __user *optval, int optlen)
+int ip_mroute_setsockopt(struct sock *sk, int optname, char __user *optval, unsigned int optlen)
 {
 	int ret;
 	struct vifctl vif;