The statistics of common-flush packets received from
this port on specified ring.
Instruction
When master-node receives valid link-down packets
or link-up packets, it will send common-flush packets,
instructing the other nodes on the ring to flush their
forwarding database.
When the nodes except master-node receive common-flush,
they will flush forwarding database. If there is any
port blocked on that node, it won't be unblocked.