libubox: update to the latest version, adds a key/value store implementation and fixes an uloop issue

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@40570 3c298f89-4303-0410-b956-a3cf2f4a3e73