DispatchIoctls(
  IN  tDEVICECONTEXT      *pDeviceContext,
  IN  PIRP                pIrp,
  IN  PIO_STACK_LOCATION  pIrpSp
  );
Routine Description:

    This Routine handles calling the OS independent routine depending on
    the Ioctl passed in.

Arguments:

    pIrp - a  ptr to an IRP

Return Value:

    NTSTATUS - status of the request