gfs2: Fix "Make glock lru list scanning safer"

gfs2: Fix "Make glock lru list scanning safer"

Commit 228804a35caa tried to add a refcount check to
gfs2_scan_glock_lru() to make sure that glocks that are still referenced
cannot be freed.  It failed to account for the bias state_change() adds
to the refcount for held glocks, so held glocks are no longer removed
from the glock cache, which can lead to out-of-memory problems.  Fix
that.  (The inodes those glocks are associated with do get shrunk and do
get pushed out of memory.)

In addition, use the same eligibility check in gfs2_scan_glock_lru() and
gfs2_dispose_glock_lru().

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>