ramips: fix MAC address assignment for RAVPower RP-WD03

ramips: fix MAC address assignment for RAVPower RP-WD03

MAC assignment based on vendor firmware:

  2.4 GHz    *:b4   (factory 0x04)
  LAN/label  *:b4   (factory 0x28)
  WAN        *:b5   (factory 0x2e)

The previously used location 0x4000 for ethernet is actually empty.

Therefore, fix the ethernet MAC address and set it as label-mac-address.

Fixes: 5ef79af4f80f ("ramips: add support for Ravpower WD03")
Suggested-by: Russell Morris <rmorris@rkmorris.us>
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>