gfs2: Always check inode size of inline inodes

Check if the inode size of stuffed (inline) inodes is within the allowed
range when reading inodes from disk (gfs2_dinode_in()).  This prevents
us from on-disk corruption.

The two checks in stuffed_readpage() and gfs2_unstuffer_page() that just
truncate inline data to the maximum allowed size don't actually make
sense, and they can be removed now as well.

Reported-by:  <syzbot+7bb81dfa9cda07d9cd9d@syzkaller.appspotmail.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>