Pull request: 3842 ptr filtering

Merge in DNS/adguard-home from 3842-fix-ptr-restrict to master

Updates #3842.

Squashed commit of the following:

commit 77bbec41c5238f8fcb0d2bb8d11910d1ac521fcd
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Nov 15 17:34:14 2021 +0300

    dnsforward: imp docs

commit c637276b5a53f5301387b7dc3035e265d0bc9418
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Nov 15 15:41:39 2021 +0300

    dnsforward: fix local ptr blocking

internal/dnsforward/stats.go

@@ -13,9 +13,8 @@ import (
 )
 
 // Write Stats data and logs
-func processQueryLogsAndStats(ctx *dnsContext) (rc resultCode) {
+func (s *Server) processQueryLogsAndStats(ctx *dnsContext) (rc resultCode) {
 	elapsed := time.Since(ctx.startTime)
-	s := ctx.srv
 	pctx := ctx.proxyCtx
 
 	shouldLog := true