ramips: Don't use a VLAN for the single ethernet port of the A5-V11.

This router only has one ethernet port, so a VLAN is useless here, now that the rt3050 TCP bug that happened without VLANs has been fixed for a very long time.

Add this router to the VLAN-less config that is used by other single-port routers.

Also fix MAC address detection code since this router has no WAN port.

Signed-off-by: Vittorio Gambaletta <openwrt@vittgam.net>