tst_qdtlscookie: use a proper 'enterLoopMSecs' instead of 'enterLoop'

It's a bit weird to calculate timeout in milliseconds and then pass
it as number of seconds ...

Pick-to: 6.1 5.15
Change-Id: I1127163ea06e49ac1b53eea6f60ee8590319bfa1
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

tests/auto/network/ssl/qdtlscookie/tst_qdtlscookie.cpp

@@ -344,7 +344,7 @@ void tst_QDtlsCookie::verifyMultipleClients()
 
     clientsToAdd = clientsToWait = 100;
 
-    testLoop.enterLoop(handshakeTimeoutMS * clientsToWait);
+    testLoop.enterLoopMSecs(handshakeTimeoutMS * clientsToWait);
     QVERIFY(!testLoop.timeout());
     QVERIFY(clientsToWait == 0);
 }