Move ubus socket path

Since OpenWrt 21.02 and newer, we need to change it, because developers of OpenWrt they decided that ubusd will run as non-root users, so they moved it.

Reference:

• https://github.com/openwrt/openwrt/commit/2dffadece9a7243a236ce7d91719787a671e23d4#diff-9536a91ee901a062b8e38e62fe624247e76fa4c268c9be6ba68af284ff0f641e

• https://git.openwrt.org/?p=project/ubus.git;a=commit;h=13a4438b4ebdf85d301999e0a615640ac4c9b0a8

cc: @msasek , @agumroian