INT 2C P - RM386 v6.00 - CLOAKING - SET PORT-TRAPPING PASSALONG
        AX = 002Dh
        DX:EBX = new I/O trapping passalong address
Return: CF clear
Note:   RM386 calls the passalong address whenever an access to a monitored
          I/O port is attempted; the handler should check whether it is a port
          that it is interested in, and if not call the previous passalong
          address (which was retrieved with AX=002Ch before installing the
          new handler)
SeeAlso: AX=0009h,AX=002Ch,INT 67/AX=5DEAh

Port-trapping passalong address called with:
        EAX = CS:IP of faulting instruction (unless executing in protected-mode
                ring 3)
        SS:EBX -> caller register structure (see AX=0009h)
                check EFLAGS V86-mode bit for type
        CX = first two bytes of I/O instruction which was trapped
        DX = port to which I/O is being performed
        CF clear
Return: CF clear if RM386 should perform I/O operation
        CF set if I/O should be skipped
Note:   RM386 skips the trapped I/O instruction, so the passalong handler
          should not modify the client CS:EIP

.