Add checkLoopbackOpts. Fix #38512

Control param checkLoopback depending on sb.config.dnsList
* if dnsList contains 127.0.0.1 - HostLoopback will be set to false. Container net namespace will be used to access loopback dns .

Fix to moby/moby#38512

Signed-off-by: Siarhei Rasiukevich <raskintech@gmail.com>

sandbox_dns_unix.go

@@ -215,7 +215,16 @@ func (sb *sandbox) setupDNS() error {
 		logrus.Infof("/etc/resolv.conf does not exist")
 	}
 
-	if len(sb.config.dnsList) > 0 || len(sb.config.dnsSearchList) > 0 || len(sb.config.dnsOptionsList) > 0 {
+			checkLoopbackOpts := func() bool {
+				for _, n := range sb.config.dnsList {
+					if n == "127.0.0.1" {
+						return true
+					}
+				}
+				return false
+			}
+
+	if checkLoopbackOpts() {
 		var (
 			err            error
 			dnsList        = resolvconf.GetNameservers(currRC.Content, types.IP)