vlan: eliminate use of dev_base_lock

Do not need to use read_lock(&dev_base_lock), use RCU instead.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>