One part of recovering from a modem crash is performing a "tag
sequence" of several IPA immediate commands, to clear the hardware
pipeline.  The sequence ends with a data transfer request on the
command endpoint (which is not otherwise done).  Unfortunately,
attempting to do the data transfer led to a hang, so that request
plus two other commands were commented out.

The previous commit fixes the bug that was causing that hang.  And
with that bug fixed we can properly issue the tag sequence when the
modem crashes, to return the hardware to a known state.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>