gluon-ebtables-filter-multicast: do not filter out Bridge Loop Avoidance

batman-adv uses gratuitous ARP packets with certain target addresses for
BLA.

Fixes #1198

package/gluon-ebtables-filter-multicast/files/lib/gluon/ebtables/110-mcast-allow-arp

+# Bridge loop avoidance
+rule 'MULTICAST_OUT -p ARP --arp-opcode Reply --arp-gratuitous --arp-mac-dst ff:43:05:00:00:00/ff:ff:ff:fc:00:00 -j RETURN'
+rule 'MULTICAST_OUT -p ARP --arp-opcode Reply --arp-gratuitous --arp-mac-dst ff:43:05:05:00:00/ff:ff:ff:ff:00:00 -j RETURN'
+
 rule 'MULTICAST_OUT -p ARP --arp-opcode Reply --arp-ip-src 0.0.0.0 -j DROP'
 rule 'MULTICAST_OUT -p ARP --arp-opcode Request --arp-ip-dst 0.0.0.0 -j DROP'
 rule 'MULTICAST_OUT -p ARP -j RETURN'