aufs: bugfix, fix the returning size of the branch attr

Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
Merge remote-tracking branch 'aufs3-standalone/aufs3.9/00base' into aufs3.9/10static
Merge branch 'aufs3.9/10static' into aufs3.9/11proc_map
Merge branch 'aufs3.9/11proc_map' into aufs3.9/18public