gluon-core: add function to gluon.util that returns all active mesh-devices

Fixes #961

gluon-core: add get_mesh_devices(uconn) to gluon.util which will return all devices being up and having proto = gluon_mesh

Backport a few patches to allow sysupgrades on mmcblk and similar block
devices.

The default abbreviation length depends on factors like user configuration,
git version and number of repository objects. Use unabbreviates IDs to make
patch generation more reproducible.

Switch from batman-adv v14/v15 debugfs to netlink

Fixes #975

The batadv debugfs requires large memory blocks to write the text debug
tables. This is inefficient for large tables like the global translation
table or the originators table.

The memory requirement can be reduced by using netlink. It copies smaller
packets in a binary format to the userspace program. The respondd module of
gluon-mesh-batman-adv-core can therefore parse larger originator tables
without causing an OOM on systems which are tight on memory.

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

The batadv debugfs requires large memory blocks to write the text debug
tables. This is inefficient for large tables like the global translation
table or the originators table.

The memory requirement can be reduced by using netlink. It copies smaller
packets in a binary format to the userspace program. gluon-status-page-api
can therefore parse larger originator tables without causing an OOM on
systems which are tight on memory.

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

This lifts batman-adv and alfred to version 2016.4.

Mesh-wide multicast requests are answered with a random delay of up to 10s.

gluon-client-bridge, gluon-mesh-batman-adv-core: switch roles of br-client and local-node interfaces

MAC and IP addresses are switched. This makes the gluon-client-bridge
package more useful for different routing protocols that don't need a
unique address on the client bridge.

As a side effect, gluon-radvd is now using the next-node address, which had
been considered before, but was dismissed to avoid having gluon-radvd
depend on gluon-next-node and gluon-mesh-batman-adv. This will be useful
for announcing default routes via gluon-radvd.

One downside is that this introduces a minor dependency on batman-adv in
gluon-respondd: the hotplug script that checked for the client interface
before will now check for local-node. This doesn't really matter: for mesh
protocols without a local-node interface, the check will do nothing (which
makes sense, as there is no interface to bind to for mesh-wide respondd).

The next-node interface may be useful with IPv4 only or even just a MAC
address. This prepares merging gluon-next-node into gluon-batman-adv-core.

Because we unconditionally appended `-i br-client` to the command line of
respondd, it wasn't restarted when br-client changed state. Now, we use a
jsonfilter expression on the network.interface dump data, similar to how the
other interface names are generated, and only add the interface to the argument
list if it is up.

* use tabs instead of spaces
* use jsonfilter for speed