vinumattach: Zero out tables after allocating them
Modify procedure at unload: if a vinum(8) has the superdev open, don't
close down. If only the daemon has it open, send the daemon a stop
request and wait for it to close the superdev, then unload.
In order to do this, create a second superdev which is opened by the
daemon. The open and close routines set a different bit in
vinum_conf.flags; otherwise the treatment is identical.
Remove opencount field in vol structure; replace by a flag bit, since
we can't count the number of opens.
Remove dead LKM grunge.
571aa87170