adblock-fast: add smartdns ipset/nftset support

adblock-fast: add smartdns ipset/nftset support

* bugfix: correct URL to config-update file
* bugfix: check if uci configs exist before chacking for changes
* add support for smartdns ipset-based blocking
* add support for smartfns nftset-based blocking
* disallow non-ascii symbols for smartdns blocking
* add check wherever fw4 restart is needed before calling
  procd_set_config_changed firewall
* improve clean-up code in resolver()
* improve case code for different resolver settings
* modify load_validate_config to allow smartdns.ipset and smartdns.nftset

Signed-off-by: Stan Grishin <stangri@melmac.ca>
(cherry picked from commit 28cd5ecf6e29fedfbd8dfcb63ea5124dac69880c)