xfs_db: teach the frag command about sparse inode chunks

xfs_db: teach the frag command about sparse inode chunks

This is the equivalent of:

ea8a48f xfs_check: process sparse inode chunks correctly

for the frag_f() command in xfs_db.

Without this, the xfs_db frag command shows corruption as it
wanders into blocks that are not inodes.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201823
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>