RIPv6 gateway list. This octet string contains the addresses
of one or more routers that could send RIPv6 updates to this
router. If a router address is included in this list,
this filter applies to RIPv6 advertisements from that router.
If non-null, The octet string contains one or more 2-tuples
of this form:
first 4 octets: interface index
next 16 octets: router address (::0 means any address)
If null, this filter applies to RIPv6 updates from any router.