Workaround for Junos 20.x OSPFv3 SNMP bug.

Some recent Junos versions, at least 20.3 and 20.4, but not 19.3 and
earlier, return a 9 in OSPFV3-MIB::ospfv3NbrRtrId when the neighbour
state is full, instead of 8 as the MIB prescribes.  Add a workaround
for that, accepting 9 as an acceptable state in case the device is
determined to be running Juniper Junos OS.  (Properly, we would only
do so if the Junos version is in a certain range, but as we don't
know exactly which versions are, or will be, affected, we just do
it for all versions of Junos.)

We haven't reported this problem to Juniper yet, but we will do so.