gluon-mesh-batman-adv: filter out all packages between bat0 and local-port

Filtering by MAC address won't filter out multicast packages like router
solicitations, causing uradvd to send out router advertisements with
maximum frequency (every 3 seconds) in active meshes, even when no local
client is actually interested in the advertisements.

Fixes #1230

package/gluon-mesh-batman-adv/files/lib/gluon/ebtables/250-next-node

 local site = require 'gluon.site_config'
 local next_node = site.next_node
 
+rule('FORWARD --logical-out br-client -i bat0 -o local-port -j DROP')
+rule('FORWARD --logical-out br-client -i local-port -o bat0 -j DROP')
+
 rule('FORWARD --logical-out br-client -o bat0 -d ' .. next_node.mac .. ' -j DROP')
 rule('OUTPUT --logical-out br-client -o bat0 -d ' .. next_node.mac .. ' -j DROP')
 rule('FORWARD --logical-out br-client -o bat0 -s ' .. next_node.mac .. ' -j DROP')