INT 6B - NPC NCSI EXTENDED SERIAL I/O - SET/RETRIEVE REQUEST/REPLY SERVICE NAME
AH = 13h
AL = virtual circuit number
CL = direction (00h get, nonzero set)
ES:BX -> buffer for/containing service name
Return: ???
Note: this function is also supported by TelAPI
SeeAlso: AH=14h,AH=15h