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>

drivers/isdn/mISDN/socket.c

@@ -415,7 +415,7 @@ data_sock_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 }
 
 static int data_sock_setsockopt(struct socket *sock, int level, int optname,
-	char __user *optval, int len)
+	char __user *optval, unsigned int len)
 {
 	struct sock *sk = sock->sk;
 	int err = 0, opt = 0;