INT 6B - NPC NCSI EXTENDED SERIAL I/O - LOG AND/OR INITIALIZE VIRTUAL CIRCUIT   
	AH = 16h
	AL = virtual circuit number
	CL = ??? switch (00h, ???)
Return: CF clear if successful
	    AL = virtual circuit number
	CF set on error
	    ???
Note:	this function is also supported by TelAPI, which always returns CF
	  clear and AL=00h
SeeAlso: AH=11h,AH=12h,AH=17h