INT 31 P - DPMI 0.9+ - SET REAL MODE INTERRUPT VECTOR
        AX = 0201h
        BL = interrupt number
        CX:DX = segment:offset of real mode handler
Return: CF clear
Note:   all memory that may be touched by a hardware interrupt handler must be
          locked down with INT 31/AX=0600h
SeeAlso: AX=0205h,AX=0600h,INT 21/AX=2505h