gfs2: Fix bugs revealed by the dct tool

Bugzilla: https://bugzilla.redhat.com/2031240 Depends: !242 (merged) Depends: https://bugzilla.redhat.com/1958140

These commits fix a number of issues revealed by Dave Teigland's dct tool for dlm testing.

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