e2fsck: Fix extent flag validity tests in pass1 on big endian boxes.

e2fsck: Fix extent flag validity tests in pass1 on big endian boxes.

Extent data is shared with the i_block[] space in the inode,
but it is always swapped on access, not when the inode is read.

In e2fsck/pass1.c we must be careful when checking validity
of the extents flag on the inode.  If the flag was set when
the inode was read & swapped, then the extents data itself
(in ->i_block[]) was NOT swapped, so testing for a valid
extent header requires some swapping first.  Then, if we
ultimately set the extents flag, all of i_block[] must be
re/un-swapped.

This passes the f_extent regression test on both ppc & x86.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>