INT 67 - Nanosoft MD386 - ENABLE/DISABLE MEMORY WRITE PROTECTION                
	AX = 5E03h
	BL = register map set number
	BH = new state (00h read-only, else read-write)
	CX = linear page number (linear address SHR 12)
Note:	setting write protection in map set 0 will cause the setting to become
	  the default for newly-allocated map sets