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 <[email protected]>

net/netlink/af_netlink.c

@@ -1150,7 +1150,7 @@ static void netlink_update_socket_mc(struct netlink_sock *nlk,
 }
 
 static int netlink_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 netlink_sock *nlk = nlk_sk(sk);