libext2fs: don't swap extent-based journal backup

libext2fs: don't swap extent-based journal backup

The f_illitable_flexbg test was failing on ppc, because
e2fsck_move_ext3_journal is doing a direct memcmp of i_block with
s_jnl_blocks, and failing.

This is because we don't swap extent data on read from disk; rather
we do it when we access the extents.  However, ext2fs_swap_super
was swapping s_jnl_blocks unconditionally, so these didn't match.

Looks like we need to treat s_jnl_blocks the same as i_block, and
swap it on access, not on read.  Except for the last i_size bit...

Reviewed-by: Andreas Dilger <adilger@sun.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>