gluon-core, gluon-l3roamd: introduce script gluon-list-mesh-interfaces that lists all currently active mesh interfaces

Not useful by itself except for testing; will be used for multi-domain
support.

[Matthias Schiffer: rename script, use for initial configuration]

While ath9k/ath10k devices can supprt VIFs with any combination of MAC addresses, there are also adapters which have a hardware MAC filter which only allows a few bits to differ. This commit changes the addresses of all VIFs to ony differ in the last 3 bits, which is required to support many Ralink/Mediatek based WLAN adapters.

Technically, the new addresses are generated by calculating an MD5 hash of the primary MAC address and using a part of this hash as a prefix for the MAC addresses.

The addresses (BSSIDs) of the AP VIFs are also reused for the LAN and WAN interfaces in mesh-on-LAN/WAN mode to reduce the number of needed addresses, and thus reduce the chance of collisions. This is not a problem as the MAC addresses of the AP VIFs are never used except as BSSID, and thus not seen by routing protocols like batman-adv.

Fixes #648

[Matthias Schiffer: rewrote commit message]

This will allow us to use its content from other languages than Lua as
well.

additional information for commit 2a93c580

Split basic radio configuration from gluon-mesh-batman-adv as this will
be required for virtually any wireless mesh protocol.

This package takes care of setting:

  - wireless channel,
  - htmode and
  - regulatory domain

gluon-mesh-batman-adv-core depends on this package.