ext4: enable the 64-bit jbd2 feature based on the 64-bit ext4 feature

Previously we were only enabling the 64-bit jbd2 feature if the number
of blocks in the file system was greater 2**32-1.  The problem with
this is that it makes it harder to test the 64-bit journal code paths
with small file systems, since a small test file system would with the
64-bit ext4 feature enable would use a 64-bit file system on-disk data
structures, but use a 32-bit journal.

This would also cause problems when trying to do an online resize to
grow the filesystem above the 2**32-1 boundary.  Fortunately the patch
to support online resize for 64-bit file systems hasn't been merged
yet, so this problem hasn't arisen in practice.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>