Pull request: 2179 ipset subdomains

Merge in DNS/adguard-home from 2179-ipset-subdomains to master

Closes #2179.

Squashed commit of the following:

commit de17caac4c2ea2bc7931f162c6dfa7822a71554f
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Jan 29 18:34:46 2021 +0300

    dnsforward: imp code, docs

commit e5ab957560bcfba80feac4b72f9b22535ecd4c7d
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Jan 26 20:43:31 2021 +0300

    dnsforward: imp code

commit 2b84d27b752832885e4896d0e75de2576e2b965b
Author: David Sheets <sheets@alum.mit.edu>
Date:   Tue Oct 6 16:34:06 2020 +0100

    dnsforward: support subdomain matching in ipset

    This is a squash of all commits in #2179.

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/AdguardTeam/urlfilter v0.14.2
 	github.com/NYTimes/gziphandler v1.1.1
 	github.com/ameshkov/dnscrypt/v2 v2.0.1
+	github.com/digineo/go-ipset/v2 v2.2.1
 	github.com/fsnotify/fsnotify v1.4.9
 	github.com/go-ping/ping v0.0.0-20201115131931-3300c582a663
 	github.com/gobuffalo/envy v1.9.0 // indirect
@@ -19,6 +20,7 @@ require (
 	github.com/karrick/godirwalk v1.16.1 // indirect
 	github.com/lucas-clemente/quic-go v0.19.3
 	github.com/mdlayher/ethernet v0.0.0-20190606142754-0394541c37b7
+	github.com/mdlayher/netlink v1.1.2-0.20201013204415-ded538f7f4be
 	github.com/mdlayher/raw v0.0.0-20191009151244-50f2db8cc065
 	github.com/miekg/dns v1.1.35
 	github.com/rogpeppe/go-internal v1.6.2 // indirect
@@ -26,6 +28,7 @@ require (
 	github.com/sirupsen/logrus v1.7.0 // indirect
 	github.com/spf13/cobra v1.1.1 // indirect
 	github.com/stretchr/testify v1.6.1
+	github.com/ti-mo/netfilter v0.4.0
 	github.com/u-root/u-root v7.0.0+incompatible
 	go.etcd.io/bbolt v1.3.5
 	golang.org/x/crypto v0.0.0-20201217014255-9d1352758620