I realized the last patch calls dev_get_by_index_rcu in a branch not
holding the rcu lock. Add the calls to rcu_read_lock and rcu_read_unlock.
Fixes: ec90ad334986 ("ipv6: Consider sk_bound_dev_if when binding a socket to a v4 mapped address") Signed-off-by: David Ahern <dsahern@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>