also, the mac address is always saved in dev->mac, so we get it
in rvlan-status also for "down" interfaces.

Example:

   wri12 (001bc509084f <-> ): state down, vlan 0, pid 0, fd -1
   wri13 (001bc5090850 <-> ): state down, vlan 0, pid 0, fd -1
   wri14 (001bc5090851 <-> ): state down, vlan 0, pid 0, fd -1
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>