INT 14 - ARTICOM - MODIFY FLOW CONTROL                                          
	AX = 800Ah
	BL = flow control type (00h none, 01h XON/XOFF, 02h RTS/CTS)
	DX = port index (COM1=0, COM2=1, ...)
Return: AX = error code, if error (see #00360)
Note:	for attached ports only!
SeeAlso: AX=8000h,AX=8003h,AX=8009h