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/packet/af_packet.c

@@ -1701,7 +1701,7 @@ static void packet_flush_mclist(struct sock *sk)
 }
 
 static int
-packet_setsockopt(struct socket *sock, int level, int optname, char __user *optval, int optlen)
+packet_setsockopt(struct socket *sock, int level, int optname, char __user *optval, unsigned int optlen)
 {
 	struct sock *sk = sock->sk;
 	struct packet_sock *po = pkt_sk(sk);