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/netrom/af_netrom.c

@@ -301,7 +301,7 @@ void nr_destroy_socket(struct sock *sk)
  */
 
 static int nr_setsockopt(struct socket *sock, int level, int optname,
-	char __user *optval, int optlen)
+	char __user *optval, unsigned int optlen)
 {
 	struct sock *sk = sock->sk;
 	struct nr_sock *nr = nr_sk(sk);