Followup of commit 634a4b20

Allow tnode_get_child_rcu() to be called either under rcu_read_lock()
protection or with RTNL held.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>