Pull request 1806: 5661-fix-protection-update-lock

Updates #5661.

Squashed commit of the following:

commit 02e83c75c8f44f084c0cb8d33b7d6a524c8c1b0e
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Apr 6 19:28:17 2023 +0300

    dnsforward: imp logs

commit 0f27265fc94f0e3b8e2dee79dbf9ab5344416c61
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Apr 6 19:18:19 2023 +0300

    dnsforward: imp locks

internal/dnsforward/dnsforward.go

@@ -9,6 +9,7 @@ import (
 	"runtime"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/AdguardTeam/AdGuardHome/internal/aghalg"
@@ -111,6 +112,10 @@ type Server struct {
 
 	isRunning bool
 
+	// protectionUpdateInProgress is used to make sure that only one goroutine
+	// updating the protection configuration after a pause is running at a time.
+	protectionUpdateInProgress atomic.Bool
+
 	conf ServerConfig
 	// serverLock protects Server.
 	serverLock sync.RWMutex