gfs2: inode directory consistency checks

gfs2: inode directory consistency checks

In gfs2_dinode_in(), only allow directories to have the GFS2_DIF_EXHASH
flag set.  This will prevent other parts of the code from treating
regular inodes as directories based on the presence of that flag.

In sweep_bh_for_rgrps() and __gfs2_free_blocks(), check if the
GFS2_DIF_EXHASH flag is set instead of checking if i_depth is non-zero.
This matches what the directory code does.  (The i_depth checks were
introduced in commit 6d3117b412951 ("GFS2: Wipe directory hash table
metadata when deallocating a directory").)

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