This new field reflects the TQ to the selected gateway.

Before this commit, if you had connectivity issues in a larger mesh,
it was a tedious task to understand which nodes are affected and which
are not. By providing this new value for each node, it becomes easier
to see which nodes are affected by the connectivity issues and which
are not.

The new field "gateway_tq" is located at the toplevel of the
statistics resource (next to "gateway" and "gateway_nexthop"):

    gluon-neighbour-info -d ::1 -r statistics
    {
        ...
        "gateway": "02:a1:71:04:09:10",
        "gateway_nexthop": "88:e6:40:20:90:10",
        "gateway_tq": 193,
        ...
    }

Also make babel match batman-adv and only emit the wireless/tunnel/other
fields when they are non-empty.

Fixes: #1783

- Split into multiple files
- Avoid alloca()

In addition this PR contains:
- split of gluon-respondd provider into multiple source files
- minor additional cleanups in gluon-mesh-babel respondd provider
  (untested, as the babel respondd provider already doesn't compile prior
  to these changes...)

We cannot add the same file (here: /lib/gluon/mesh-batman-adv/compat) to
two, installed packages. Therefore, instead of determining the compat
version number from this file, infer it from the batman-adv release
version number instead.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>

The commit ee63ed42fe6c ("gluon-mesh-batman-adv: List neighbors with
non-best direct link") removed the check whether a neighbor has the
BATADV_ATTR_FLAG_BEST set. But consumers may still want to filter out or
mark neighbors which don't have this flag set. To assist with such a
feature, enhance the neighbor object with an extra boolean "best" attribute
which stores whether the BATADV_ATTR_FLAG_BEST was found or not.

Reported-by: Vincent Wiemann <webmaster@codefetch.de>

Links between two direct neighbors are not always the best route between
these devices. The flag BATADV_ATTR_FLAG_BEST would not be set for these
originator entries and the respondd module would just ignore this entry.

This causes missing links in meshviewer and similar tools. And when the
link quality is nearly equal and but fluctuates slightly, these links will
from time to time appear and disappear on the map.

Fixes: 2e0e24a9 ("announce neighbours using alfred/gluon-announce")

The amount of local wifi clients is currently counted by two different
ways:

* asking the kernel wifi layer for the number of of clients on 2.4GHz and
  5GHz band
* asking batman-adv for the number of non-timed out entries in the local
  translation table with WiFi flag

The number of wifi24+wifi5 and the number of TT wifi client counts are
reported via respondd to various consumers. The ffrgb meshviewer is
displaying these values as:

* 2,4 GHz: wifi24
* 5 GHz: wifi5
* other: (TT local wifi+non-wifi clients) - (wifi24 + wifi5)

But the local translation table is holding entries much longer than the
wifi layer. It can therefore easily happen that a wifi client disappears in
the kernel wifi layer and batman-adv still has the entry stored in the
local TT.

The ffrgb meshviewer would then show this count in the category "other".
This often results in confusions because "other" is usually for ethernet
clients. And nodes with a frequently disappearing larger group of clients
(near bus stations or larger intersections) often show most clients under
the group "other" even when this devices doesn't have a LAN ethernet port.

It is better for presentation to calculate the number of total wifi clients
by summing up wifi24 + wifi5. And getting the number of total clients (non
wifi + wifi) by adding the result of the previous calculation to the sum of
non-wifi client in the local batman-adv translation table.

Fixes: 89a9d813 ("gluon-mesh-batman-adv-core: Announce client count by frequency")
Reported-by: Pascal Wettin <p.wettin@gmx.de>

At least the ifindex and the flags fields can be larger than 0xff.

Fixes #1523

Signed-off-by: Sven Eckelmann <sven@narfation.org>

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.