ramips: fix used MAC addresses for Phicomm K2P

ramips: fix used MAC addresses for Phicomm K2P

The factory partition of the Phicomm K2P contains two MAC addresses.
The lower MAC address is at offset 0xe006 and the higher one is at
offset 0xe000.

Use the lower MAC address as base mac-address which the switch driver
increments by one for the second (wan) vlan.

The MAC addresses are still inverted in contrast to the stock firmware
where the lower MAC address is used for wan. But at least the use of a
MAC address not intended/reserved for this particular board is fixed.

Signed-off-by: Jiawei Wang <me@jwang.link>