Fixes #1130

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

In preparation for Babel support.

We also make use of the boolean support of simple-uci to make scripts
clearer.

Fixes #842

Switch to:

1. WAN
2. LAN
3. Mesh VPN

As WAN and LAN are setup in gluon-mesh-batman-adv-core (and will be moved
to gluon-core), while the mesh VPN has its own package, giving WAN and LAN
the first indices is preferable.

Some drivers (mt76) don't support arbitrary MAC addresses. Use the
addresses provided by the driver (avoiding the primary address) by default,
but fall back to our has-based scheme when the driver doesn't provide
(enough) addresses.

Most doubles that are delivered via respondd have limited input
precision, but are converted with up to 17 digits of precision. That can
cause ugly blowups like 0.2800000000000001 in the output, which is
avoided by specifying better format strings (like "%.2f" in most cases).

This was causing "recursive dependency" errors and potentially broken
configurations.

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]

Avoid commiting configs inbetween to decrease number of flash writes.

Fixes #714.

gluon-announced and gluon-announce are merged to gluon-respondd.

The Gluon-specific functions of the gluon-simple-tc package are moved to
gluon-mesh-vpn-fastd.

Apart from replacing a patch for the former by two patches for latter,
this involved minimal adaptations of the lua scripts in the following
packages:

* gluon-announce
* gluon-announced
* gluon-mesh-batman-adv-core
* gluon-status-page

This will require site.mk to explicitly pull in the gluon-setup-mode and
gluon-config-mode-core packages.

This adds basic peer statistics to statistics.d:

    "mesh_vpn": {
      "muehlentor": {
        "established": 23.8 // seconds
      },
      "huextertor": null,
      "holstentor": null
    }

Moving the scripts to a common directory not only vastly simplifies the
zzz-gluon-upgrade script, but also allows to define an ordering of such
scripts across packages.

This patch allows fastd's enabled flag's default value to be set from
site.conf.

Previously, the config-mode was responsible for generating the fastd
secret. This patch sets the default secret to "generate" causing a
secret to be generated on its first use (e.g. show_key or start).

This also changes the info page (in Expert Mode) to show "n/a" when the
public key is not yet available.

The support is still very limited (IPv6-only DNS on WAN doesn't work yet), and
we now need fastd running as root, but apart from that, is should work.

All announce.d scripts have been moved to /lib/gluon/announce/announce.d
The script /lib/gluon/announce/announce.lua will collect all information
and output json.