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/bluetooth/sco.c

@@ -644,7 +644,7 @@ static int sco_sock_sendmsg(struct kiocb *iocb, struct socket *sock,
 	return err;
 }
 
-static int sco_sock_setsockopt(struct socket *sock, int level, int optname, char __user *optval, int optlen)
+static int sco_sock_setsockopt(struct socket *sock, int level, int optname, char __user *optval, unsigned int optlen)
 {
 	struct sock *sk = sock->sk;
 	int err = 0;