ext4: add more mount time checks of the superblock

commit bfe0a5f47ada40d7984de67e59a7d3390b9b9ecc upstream.

The kernel's ext4 mount-time checks were more permissive than
e2fsprogs's libext2fs checks when opening a file system.  The
superblock is considered too insane for debugfs or e2fsck to operate
on it, the kernel has no business trying to mount it.

This will make file system fuzzing tools work harder, but the failure
cases that they find will be more useful and be easier to evaluate.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>