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.

Fixes #941

The interfaces were accidentially switched when the CPE210 was separated
from the CPE510 code.

If cookies are disabled, the Statuspage only displays an empty ("Not connected")
This checks if the localStorage API is available and working and only uses it in this case
Also allows better backwards compatibility.

Fixes #886

If next_node.ip4 is not set or gluon-next-node is not used, prefix4 will
now be optional as well.

None of them are used by modern browsers anymore, so it's safe to remove them.

Fixes #834

Fixes #842

Users may have defined additional mesh interfaces. Properly migrate these
to avoid subtly breaking the network config (and make them ready for new
mesh protocols).

gluon-client-bridge: add LAN interfaces to client bridge by default (instead of doing this in the batman-adv-specific scripts)

This allows to weaken the gluon-mesh-batman-adv-core dependency of
gluon-luci-portconfig to gluon-client-bridge.

This new protocol will allow configuring mesh interfaces independently of
the used mesh protocol.

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.

Fixes #854

Fixes #414

Allows weird release numbers, models and site names, and prepares support
for pretty hostnames.

and add documentation

Fixes #862

Just like we enabled multicast snooping on the batman-adv client bridge
again, let's do the same for the WAN side.

With one exception: The IGMP/MLD querier is kept disabled to avoid
becoming too "bossy"/"noisy" on a foreign network. The main router on
the WAN side should perform querying and by that enable
IGMP/MLD/snooping if it considers this appropriate there.

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

A few issues with the bridge snooping were identified and fixed
upstream in OpenWRT:

* "firewall: Allow IGMP and MLD input on WAN" (r45613)
* "kernel: bridge: backport two snooping related patches" (r45783)
* netifd: "bridge: Fix multicast_to_unicast feature by hairpin+isolate"
  (OW: "netifd: update to the latest version, adds multicast-to-unicast fixes" (r46719))
* "kernel: bridge, multicast-to-unicast: assign src after pskb_may_pull()" (r46721)
* "kernel: bridge, multicast-to-unicast: fix echoes on STA" (46765)

These have very likely caused issues with the bridge snooping before,
which led to disabling it in the past. Let's reenable the multicast
snooping now that they were fixed for reduced multicast overhead on the
wifi.

Advantages are the following:

This mildly reduces overhead on the mesh layer. And significantly reduces
overhead on the AP interface and therefore significantly increases
available airtime (the currently most significant scalability bottleneck).

Secondly removes an easy, often accidental node-local Denial-of-Service
vector based on multicast flooding / streaming.

Thirdly, makes node-local multicast streaming feasible.

Finally should noticably increase battery life of mobile devices.

Note: bridge querier is disabled for br-wan. We want to avoid becoming
too "bossy"/"noisy" on a foreign network.

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