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/inet_connection_sock.c

@@ -714,7 +714,7 @@ int inet_csk_compat_getsockopt(struct sock *sk, int level, int optname,
 EXPORT_SYMBOL_GPL(inet_csk_compat_getsockopt);
 
 int inet_csk_compat_setsockopt(struct sock *sk, int level, int optname,
-			       char __user *optval, int optlen)
+			       char __user *optval, unsigned int optlen)
 {
 	const struct inet_connection_sock *icsk = inet_csk(sk);