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/hci_sock.c

@@ -466,7 +466,7 @@ drop:
 	goto done;
 }
 
-static int hci_sock_setsockopt(struct socket *sock, int level, int optname, char __user *optval, int len)
+static int hci_sock_setsockopt(struct socket *sock, int level, int optname, char __user *optval, unsigned int len)
 {
 	struct hci_ufilter uf = { .opcode = 0 };
 	struct sock *sk = sock->sk;