Pull request: 3225 bsd dhcp

Merge in DNS/adguard-home from 3225-bsd-dhcp to master

Closes #3225.
Closes #3417.

Squashed commit of the following:

commit e7ea691824c7ebc8cafd8c9e206679346cbc8592
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Aug 12 17:02:02 2021 +0300

    all: imp code, docs

commit 5b598fc18a9b69a0256569f4c691bb6a2193dfbd
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Aug 12 16:28:12 2021 +0300

    all: mv logic, imp code, docs, log changes

commit e3e1577a668fe3e5c61d075c390e4bd7268181ba
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Aug 12 14:15:10 2021 +0300

    dhcpd: imp checkother

commit 3cc8b058195c30a7ef0b7741ee8463270d9e47ff
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Wed Aug 11 13:20:18 2021 +0300

    all: imp bsd support

scripts/make/go-lint.sh

@@ -114,6 +114,7 @@ underscores() {
 		-e '_bsd.go'\
 		-e '_darwin.go'\
 		-e '_freebsd.go'\
+		-e '_openbsd.go'\
 		-e '_linux.go'\
 		-e '_little.go'\
 		-e '_others.go'\