net/packet: constify __packet_get_status() argument

struct packet_sock  is only read.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/packet/af_packet.c

@@ -384,7 +384,7 @@ static void __packet_set_status(struct packet_sock *po, void *frame, int status)
 	smp_wmb();
 }
 
-static int __packet_get_status(struct packet_sock *po, void *frame)
+static int __packet_get_status(const struct packet_sock *po, void *frame)
 {
 	union tpacket_uhdr h;