Don't skip EXTENT_UNKNOWN extents

It seems btrfs will mark delalloc extents with this flag. Since we don't yet
know what type of extent it will result in, we should try for dedupe instead
of marking it to be skipped.

Signed-off-by: Mark Fasheh <mfasheh@suse.de>
debug print fiemap extent flags in filerec_count_shared()

Signed-off-by: Mark Fasheh <mfasheh@suse.de>