base-files: depend on jsonfilter and rewrite network.sh to use it

Switches /lib/functions/network.sh from jshn based json parsing to
jsonfilter expression while keeping the existing api.

Expensive methods like "network_find_wan" are up to 20x faster now.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@41281 3c298f89-4303-0410-b956-a3cf2f4a3e73