Closes #2934. Squashed commit of the following: commit 856ea4ec0c3ffb1da447b93260da90d37cd5d45d Author: Ainar Garipov <A.Garipov@AdGuard.COM> Date: Thu Apr 15 17:39:46 2021 +0300 dnsforward: imp spacing commit fa748e5a26cb6a38b5f87c5498287cb734ce7a59 Author: Ainar Garipov <A.Garipov@AdGuard.COM> Date: Thu Apr 15 17:33:44 2021 +0300 dnsforward: imp code commit 771ba0de449faffff1cea523e8bbcc1039c992db Author: Ainar Garipov <A.Garipov@AdGuard.COM> Date: Thu Apr 15 17:06:03 2021 +0300 all: do not use dhcp clients when server is off