MFC r196822, r196823, r196824:

MFC r196822, r196823, r196824:

Remove 'ad:' prefix from disk serial number. We don't want serial number
to change when we reconnect the disk in a way that it is accessible through
CAM for example.

Discussed with:	trasz

Simplify g_disk_ident_adjust() function and allow any printable character
in serial number.

Discussed with:	trasz
Obtained from:	Wheel Sp. z o.o. (http://www.wheel.pl)

Make serial numbers of daX disks visible by GEOM.

No objections from:	scottl
Obtained from:	Wheel Sp. z o.o. (http://www.wheel.pl)

Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/stable/8@197217 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f