Add Support for the ALFA Hornet UB and similar devices

The Hornet UB is sold at least in the varieties. Without case it is a Hornet UB, with case and without connected USB port it is called AP121. If the USB port is present this device is called AP121U.
We have a AP121U in our mesh http://meshviewer.chemnitz.freifunk.net/#!v:m;n:00c0ca6efffa

Preparations for Multicast Snooping

docs: fix typo in upgrade.rst

Add support for TP-Link TL-WA7510N

This CPE is supported by OpenWRT and already running in Chemnitz

This include wasn't actually missing, but well hidden behind the iwinfo.h
include. Make this more obvious.

Adopt the according modifications to the default firewall settings of
the WAN interface from OpenWRT, revision 45613.

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

An IGMP/MLD domain split will prevent us from being able to track
multicast listeners on other nodes.

Therefore we need to always hand any multicast packets we received from
local clients to batman-adv. With bridge multicast snooping disabled,
the current setting in Gluon, this is already the case.

However, in preparation to enabling multicast snooping, we need to
enforce forwarding towards batman-adv by setting the bridge port
option "multicast_router" to 2.

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

Backport of rr46271 and r46922.

Based-on-patch-by: Julian Kornberger <jk+github@digineo.de>

git submodules

Possibility to work with git submodules

We use our own firmware package.

We got most of our patches backported by upstream :)

It is not supported by all browsers yet.

Also change load display always to display 2 decimal digits (as it is read
from the kernel with 2 decimal digits).

Fixes #606

ar71xx-generic: add support for TP-Link MR13U

notUpdated is a Set, to a for-in loop doesn't work.

Fixes #657

Make bandwidth limits unsigned; trim numbers, the validator accepts
trailing whitespace.

This script will analyze the dependencies of Gluon's packages and output
them as a dot graph.

Backport of r48279

fix rescue mode on wdr4900

Backport of r48793

This option will make the generated commit IDs deterministic, greatly
reducing the number of repository objects created when calling `make
update` repeatedly.

brcm2708-gpu-fw: move pkg build dir to kernel build dir to fix rebuild bugs after cleaning the kernel tree

Backport of r48732

Mobile browsers will often show or hide the address bar while scrolling.
This causes resize events which would often reset the signal graphs.

Fixes #662

The bootloader of AirOS 5.6.x doesn't remove the flash protection for us,
so we have to do this ourselves.

This should fix problems with flashing from AirOS 5.6.x.