ath79-generic: (re)add support for UniFi AC Mesh

[AiyionPrime]

• must be flashable from vendor firmware
  • webinterface
  • tftp
  • other: (downgrade), scp than ssh syswraper...
• must support upgrade mechanism
  • must have working sysupgrade
    • must keep/forget configuration (if applicable)
      think sysupgrade [-n] or firstboot
  • must have working autoupdate
    usually means: gluon profile name must match image name
• reset/wps/phone button must return device into config mode
• primary mac should match address on device label (or packaging) (https://gluon.readthedocs.io/en/latest/dev/hardware.html#notes)
• wired network
  • should support all network ports on the device
  • must have correct port assignment (WAN/LAN)
    • On devices supplied via PoE, there is usually no explicit WAN/LAN labeling on the hardware.
      The PoE input should be the WAN port in this case.
• wifi (if applicable)
  • association with AP must be possible on all radios
  • association with 802.11s mesh must be working on all radios
  • ap/mesh mode must work in parallel on all radios
• led mapping
  • power/sys led (critical, because led definitions are setup on firstboot only)
    • lit while the device is on
    • should display config mode blink sequence
      (https://gluon.readthedocs.io/en/latest/features/configmode.html)
  • radio leds
    • should map to their respective radio
    • should show activity
  • switchport leds
    • ~~should map to their respective port (or switch, if only one led present) ~~
    • should show link state and activity
• outdoor devices only
  • added board name to is_outdoor_device function in package/gluon-core/luasrc/usr/lib/lua/gluon/platform.lua

[AiyionPrime]

Migration worked without issues.