dlm: Avoid that dlm_release_lockspace() incorrectly returns -EBUSY

dlm: Avoid that dlm_release_lockspace() incorrectly returns -EBUSY

When dlm_release_lockspace(ls, 1) is invoked on a busy system
immediately after the last dlm_unlock() AST has finished it can occur
that lkb_idr_is_local() is invoked for the unlocked LKB since removal
from ls_lkbidr only occurs after the AST has returned. If that happens
dlm_release_lockspace(ls, 1) will return -EBUSY instead of releasing
the lockspace. Fix this race condition by changing lkb_idr_is_local()
such that it only returns true for LKB's that have not yet been
unlocked.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: David Teigland <teigland@redhat.com>