gluon-mesh-batman-adv-core: reenable multicast snooping

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>

package/gluon-mesh-batman-adv-core/luasrc/lib/gluon/upgrade/310-gluon-mesh-batman-adv-core-mesh

@@ -37,7 +37,7 @@ end
 
 uci:set('network', 'client', 'proto', 'dhcpv6')
 uci:set('network', 'client', 'reqprefix', 'no')
-uci:set('network', 'client', 'igmp_snooping', 0)
+uci:delete('network', 'client', 'igmp_snooping')
 uci:set('network', 'client', 'robustness', 3)
 uci:set('network', 'client', 'query_interval', 2000)
 uci:set('network', 'client', 'query_response_interval', 500)