wimax/i2400m: queue device's report until the driver is ready for them

The i2400m might start sending reports to the driver before it is done
setting up all the infrastructure needed for handling them.

Currently we were just dropping them when the driver wasn't ready and
that is bad in certain situations, as the sync between the driver's
idea of the device's state and the device's state dissapears.

This changes that by implementing a queue for handling
reports. Incoming reports are appended to it and a workstruct is woken
to process the list of queued reports.

When the device is not yet ready to handle them, the workstruct is not
woken, but at soon as the device becomes ready again, the queue is
processed.

As a consequence of this, i2400m_queue_work() is no longer used, and
thus removed.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>