s390/qeth: merge qeth_reply struct into qeth_cmd_buffer

Except for card->read_cmd, every cmd we issue now passes through
qeth_send_control_data() and allocates a qeth_reply struct. The way we
use this struct requires additional refcounting, and pointer tracking.

Clean up things by moving most of qeth_reply's content into the main
cmd struct. This keeps things in one place, saves us the additional
refcounting and simplifies the overall code flow.
A nice little benefit is that we can now match incoming replies against
the pending requests themselves, without caching the requests' seqnos.

The qeth_reply struct stays around for a little bit longer in a shrunk
form, to avoid touching every single callback.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>