net: Make the copy length in af_packet sockopt handler unsigned

fixed upstream in commit b7058842 in a different way

The length of the to-copy data structure is currently stored in
a signed integer. However many comparisons are done with sizeof(..)
which is unsigned. It's more suitable for this variable to be unsigned
to make these comparisons more naturally right.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

net/packet/af_packet.c

@@ -1836,7 +1836,7 @@ packet_setsockopt(struct socket *sock, int level, int optname, char __user *optv
 static int packet_getsockopt(struct socket *sock, int level, int optname,
 			     char __user *optval, int __user *optlen)
 {
-	int len;
+	unsigned int len;
 	int val;
 	struct sock *sk = sock->sk;
 	struct packet_sock *po = pkt_sk(sk);
@@ -1849,7 +1849,7 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
 	if (get_user(len, optlen))
 		return -EFAULT;
 
-	if (len < 0)
+	if ((int)len < 0)
 		return -EINVAL;
 
 	switch (optname) {