Function 2     : Set Interrupt number.

Entry          : BX = 2.
                 AX = Interrupt number for the DMA.
Exit           : None.

This function sets the interrupt number used for the driver during
a DMA transfer.

Four interrupts, interrupt 2, 3, 5 and 7, are available. Developers
should also allow users to specify their choice. The two methods
suggested earlier can be used here too. If second method is used,
the interrupt number used is stored as  a char type (1 byte) at the
offset 32 hex.

Again, the default installed interrupt number is used if this
function is not invoked to change it. The factory default interrupt
number is 3.

This function must be invoked before the "Initialize Driver"
function.