BBSIM: OMCI extended message set - support of table attribute retrieval

If the OMCC version of a BBSIM ONU is configured to a value that supports the OMCI extended message set (see VOL-4678), OMCI requests for table attribute retrieval - especially "Get next" requests - in extended message format shall be answered with the corresponding OMCI responses in extended message format. It is assumed that the number of necessary "Get next" messages is significantly reduced due to the greater length of the message content (1966 vs 29 bytes).