openonuAdapterGo: OMCI extended message set - support MIB upload

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 "MIB upload" and "MIB upload next" shall be send in extended message format. Openonu-adapter has to be able to evaluate corresponding OMCI responses in extended message format. It is assumed that the number of necessary "MIB upload next" messages is significantly reduced due to the greater length of the message content (1966 vs 29 bytes).