Update probe flow so that devices with lbp can also disable disksort.

Ensure that delete_available is reset so re-probes after a media change,
to one with different delete characteristics, will result in the correct
methods being flagged as available.

Make all ccb state changes use a consistent flow:
* free()
* xpt_release_ccb()
* softc->state = <new state>
* xpt_schedule()

Reviewed by:	mav
Approved by:	pjd (mentor)
MFC after:	1 week
Fix probe in progress check in dareprobe

Reviewed by:	mav
Approved by:	pjd (mentor)
MFC after:	1 week