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/ieee802154/dgram.c

@@ -414,7 +414,7 @@ static int dgram_getsockopt(struct sock *sk, int level, int optname,
 }
 
 static int dgram_setsockopt(struct sock *sk, int level, int optname,
-		    char __user *optval, int optlen)
+		    char __user *optval, unsigned int optlen)
 {
 	struct dgram_sock *ro = dgram_sk(sk);
 	int val;