btrfs: extended inode refs

btrfs: extended inode refs

This patch adds basic support for extended inode refs. This includes support
for link and unlink of the refs, which basically gets us support for rename
as well.

Inode creation does not need changing - extended refs are only added after
the ref array is full.

Reviewed-by: Jan Schmidt <list.btrfs@jan-o-sch.net
Signed-off-by: Mark Fasheh <mfasheh@suse.de>