A count of the number of times a REGISTER_ACK MPCP
frames reception occurs. A single counter at the ONU and
a set of counters, one for each LLID, at the OLT.
Increment the counter by one for each REGISTER_ACK MPCP
frame received for each LLID, as defined in [802.3ah]
clause 64. This counter is mandatory for an ONU and for
an OLT. At the ONU the value should be zero.