OPENDJ-1560 modify/modifyrdn operations are not working in mix replication topology

There is a mismatch between code before and after r10757.
This is affecting 2.6.x and 2.6.next OpenDJ servers communicating with each other.
Before r10757, serialized ModifyMsg included a zero separator after byte arrays, after r10757 it did not.
This change is introducing back the zero separator.

ModifyMsg.java:
In getBytes_V45(), appended the zero byte separator after byte arrays + adapted decodeBody_V4() code for it.