ext4: Ignore i_file_acl_high unless EXT4_FEATURE_INCOMPAT_64BIT is present

Don't try to look at i_file_acl_high unless the INCOMPAT_64BIT feature
bit is set.  The field is normally zero, but older versions of e2fsck
didn't automatically check to make sure of this, so in the spirit of
"be liberal in what you accept", don't look at i_file_acl_high unless
we are using a 64-bit filesystem.

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