When a Gluon node is used to connect to an uplink router/DHCP server (for
example in deployments without VPN tunnels), the gw_mode must be set to
server; this should be preserved on upgrades.

Fixes #1196

[Matthias Schiffer: move to proto_gluon_bat0_setup() and default to BATMAN_IV]

Improve error handling a bit, and fix upgrade for some (unsupported or
broken) targets.

`make show-release` can be used to discover the current release in scripts.

This reverts commit dcff6802.

The added debug information is stripped of during packaging, so it does not
increase the package size. It does however slightly change offsets in the
code, preventing the weird ash segfaults we've been seeing. Also, if the
issue returns, we'll have debug information matching the coredumps.

A bug in batman-adv can lead to a large amount of management traffic being
exchanged between nodes when the multicast optimizations are enabled,
effectively making the mesh unusable. It's safer to disable the feature
for now, until we have a real fix.

sha512sum doesn't add much code that is not also used by sha256sum, but the
change of the configuration hides the segfault issue described in:

  https://bugs.lede-project.org/index.php?do=details&task_id=822

While the issue only seemed to affect dhcpv6.script, it would clutter /tmp
with coredumps, eventually leading to OOM.

This patch got lost in the OpenWrt -> LEDE transition and fixes flash
writes on new UBNT PicoStations.

The used nodejs 4.4.5 needs at least GCC 4.8 to be build
https://github.com/nodejs/node/blob/v4.x/BUILDING.md



Signed-off-by: Matthias Fritzsche <matthias@chemnitz.freifunk.net>
[Matthias Schiffer: moved information to the first section]

Allow the autoupdater to work when updating from the removed targets.

iptables will be pulled in anyways.

These devices have never actually existed; the corresponding support
strings have been removed from the stock firmwares as well.

It seems the device was lost during the OpenWrt -> LEDE migration.