INT 21 u - LAN Manager Enhanced DOS - DosMakeMailslot                           
	AX = 5F4Dh
	BX = message size
	CX = mailslot size (must be bigger than message size by at least 1)
			   (minimum 1000h, maximum FFF6h)
			   (buffer must be 9 bytes bigger than this)
	DS:SI -> name
	ES:DI -> memory buffer
Return: CF clear if successful
	    AX = handle
	CF set on error
	    AX = error code
SeeAlso: AX=5F4Eh,AX=5F4Fh,AX=5F50h,AX=5F51h