INT 21 - Phar Lap 386/DOS-Extender - CHANGE SEGMENT ATTRIBUTES

	AX = 2514h
	BX = segment selector of descriptor in GDT or LDT
	CL = new access-rights byte
	CH = new use-type bit (USE16 or USE32)
Return: CF clear if successful
	CF set on error
	    EAX = error code
		09h invalid selector in BX
SeeAlso: AX=2515h,INT 31/AX=0009h