packet: free packet_rollover after synchronize_net

Destruction of the po->rollover must be delayed until there are no
more packets in flight that can access it. The field is destroyed in
packet_release, before synchronize_net. Delay using rcu.

Fixes: 0648ab70afe6 ("packet: rollover prepare: per-socket state")

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/packet/internal.h b/net/packet/internal.h
index c035d26..e20b3e8 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -89,6 +89,7 @@
 
 struct packet_rollover {
 	int			sock;
+	struct rcu_head		rcu;
 	atomic_long_t		num;
 	atomic_long_t		num_huge;
 	atomic_long_t		num_failed;