ramips: correct/add Phicomm K2x WAN/label MAC address

ramips: correct/add Phicomm K2x WAN/label MAC address

Phicomm K2G:
add missing label_mac

Phicomm PSG1218A & PSG1218B:
The previous wan mac was set as factory@0x28 +1 (originally based
on the default case for the ramips target), but the correct wan mac
is factory@0x28 -1, being equal to factory@0x2e.

Signed-off-by: Shiji Yang <yangshiji66@qq.com>
[minor commit title/message adjustments]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
(cherry picked from commit 55263ffedbe1d20f005febbc973a7353240d1741)