INT 2F - INTERLNK - CHECK IF PORTIBM PC Portable (uses same BIOS as XT) IN USE
	AX = 5602h
	DX = magic value FFFFh
	BL = instance number (00h=any, 01h=first loaded, etc.)
	CX = base port address of COM / LPTAbbreviation for Line PrinTer. port to check
Return: (as for AL=00h if port in use for a redirected drive)
SeeAlso: AX=5600h