ip6mr: do not get a device reference in pim6_rcv()

pim6_rcv() is called under rcu_read_lock(), there is
no need to use dev_hold()/dev_put() pair.

IPv4 side was handled in commit 55747a0a
("ipmr: __pim_rcv() is called under rcu_read_lock")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6mr.c

@@ -554,7 +554,6 @@ static int pim6_rcv(struct sk_buff *skb)
 	read_lock(&mrt_lock);
 	if (reg_vif_num >= 0)
 		reg_dev = mrt->vif_table[reg_vif_num].dev;
-	dev_hold(reg_dev);
 	read_unlock(&mrt_lock);
 
 	if (!reg_dev)
@@ -570,7 +569,6 @@ static int pim6_rcv(struct sk_buff *skb)
 
 	netif_rx(skb);
 
-	dev_put(reg_dev);
 	return 0;
  drop:
 	kfree_skb(skb);