netifd: update to latest version, add bridge_empty option

with this option enabled it's possible to create empty bridges

Signed-off-by: Luka Perkov <luka@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37318 3c298f89-4303-0410-b956-a3cf2f4a3e73