INT 14 - TelAPI - "telportosn" - GET SESSION NUMBER FOR COM PORTIBM PC Portable (uses same BIOS as XT)
	AH = E9h
	DX = serial port number (0000h-0003h = COM1-COM4)
Return: AX >= 0000h session number
	AX < 0000h error code (see #00397)
SeeAlso: AH=E0h,AH=E8h,AH=EAh,AX=FF00h