Pull request: all: mv some utilities to netutil

Merge in DNS/adguard-home from mv-netutil to master

Squashed commit of the following:

commit 5698fceed656dca7f8644e7dbd7e1a7fc57a68ce
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Aug 9 15:44:17 2021 +0300

    dnsforward: add todos

commit 122fb6e3de658b296931e0f608cf24ef85547666
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Aug 9 14:27:46 2021 +0300

    all: mv some utilities to netutil

internal/dnsforward/http.go

@@ -9,11 +9,11 @@ import (
 	"strings"
 	"time"
 
-	"github.com/AdguardTeam/AdGuardHome/internal/aghnet"
 	"github.com/AdguardTeam/dnsproxy/proxy"
 	"github.com/AdguardTeam/dnsproxy/upstream"
 	"github.com/AdguardTeam/golibs/errors"
 	"github.com/AdguardTeam/golibs/log"
+	"github.com/AdguardTeam/golibs/netutil"
 	"github.com/AdguardTeam/golibs/stringutil"
 	"github.com/miekg/dns"
 )
@@ -443,7 +443,7 @@ func separateUpstream(upstreamStr string) (upstream string, useDefault bool, err
 			continue
 		}
 
-		err = aghnet.ValidateDomainName(host)
+		err = netutil.ValidateDomainName(host)
 		if err != nil {
 			return "", false, fmt.Errorf("domain at index %d: %w", i, err)
 		}