The set of ports that are configured to join a multicast
group. It has the information of up to 2k ports with the
port number starting from the information indicated in
cisMcastPortRangeIndex object of the same row. For
example, if the value of cisMulticastGroupConfPortRange is
'twoKto4K', the port number indicated in this object starting
from 2049 and ending to 4096.
A port number is the value of dot1dBasePort for the port
in the BRIDGE-MIB (RFC 4188).