The Airgateway LR is the same device as the normal Airgateway but with an detachable antenna. The Pro version is a cheap dual band device.

gluon-core: dns-cache documentation polish
Now its clear that upstreams severs normally means "community gateways".
* added cacheentries to description
* made upstream server description more general
* description of the A and AAAA-records for next_node added
* mention of Cache not being allocated when not set in site.conf 
* dns-cache doku polish

For simplicity, we don't use different MTUs for compat 14 and 15 anymore,
there's no harm in using 1532 for batman-adv-legacy as well.

The fastd_mesh_vpn site.conf section is renamed to mesh_vpn.fastd.

This was introduced in ffhh-packages at https://github.com/freifunkhamburg/ffhh-packages/tree/master/gluon-config-mode-reboot-ffhh

_translate() will return nil when no match is found.

Add missing trailing `,` in simple_tc section and change the order of ingress and egress to default format used by Gluon.

These devices don't have unique MAC addresses with OpenWrt/LEDE at the moment
(see #993).

Fixes #961