Communicating Applications Spec - Get/set autoreceive

        Entry:
          AX = CB0Fh
          DL = subfunction
              00h get current autoreceive state
              01h set autoreceive state
                  DH = number of rings before answer, 00h = never
        Return:
          AX = 0000h autoreceive disabled
             = N   number of rings before answer
             < 0   error code (see AX=CB01h)