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>
diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index b030125..555d9da 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -1698,7 +1698,7 @@
 	return bt_sock_recvmsg(iocb, sock, msg, len, flags);
 }
 
-static int l2cap_sock_setsockopt_old(struct socket *sock, int optname, char __user *optval, int optlen)
+static int l2cap_sock_setsockopt_old(struct socket *sock, int optname, char __user *optval, unsigned int optlen)
 {
 	struct sock *sk = sock->sk;
 	struct l2cap_options opts;
@@ -1755,7 +1755,7 @@
 	return err;
 }
 
-static int l2cap_sock_setsockopt(struct socket *sock, int level, int optname, char __user *optval, int optlen)
+static int l2cap_sock_setsockopt(struct socket *sock, int level, int optname, char __user *optval, unsigned int optlen)
 {
 	struct sock *sk = sock->sk;
 	struct bt_security sec;