docs: update link to site repository of Freifunk MWU

Fixes #886

If next_node.ip4 is not set or gluon-next-node is not used, prefix4 will
now be optional as well.

The GLUON_ATH10K_MESH must be set to 11s or ibss; when it is not set,
ath10k device images won't be built at all. This also allows us to remove
the BROKEN flag for ath10k devices, as the GLUON_ATH10K_MESH variable is
sufficient to avoid ath10k devices if desired.

Fixes #864

The MR1750 and OM5P-AC devices are based on ath9k SoCs and an external
ath10k chip. All devices which are using ath10k should be marked as broken
due to deficits in their IBSS support.

Signed-off-by: Sven Eckelmann <sven.eckelmann@open-mesh.com>

None of them are used by modern browsers anymore, so it's safe to remove them.

Fixes #834

Fixes #842

Users may have defined additional mesh interfaces. Properly migrate these
to avoid subtly breaking the network config (and make them ready for new
mesh protocols).

gluon-client-bridge: add LAN interfaces to client bridge by default (instead of doing this in the batman-adv-specific scripts)

This allows to weaken the gluon-mesh-batman-adv-core dependency of
gluon-luci-portconfig to gluon-client-bridge.

This new protocol will allow configuring mesh interfaces independently of
the used mesh protocol.

[Matthias Schiffer: changed the text a bit]