s390/qeth: send IDX cmds via qeth_send_control_data()

This converts the IDX code to use qeth_send_control_data(), replacing
a bunch of duplicated IO code and unbounded waits. It also allows the
IDX sequence to benefit from the improved timeout & notify
infrastructure, so that we can eliminate the DOWN -> ACTIVATING -> UP
transition in the channel state machine.

The patch looks rather big, but most of it is a straight-forward
conversion of the old IDX cmd setup & callbacks to the new model.

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