tst_QTcpSocket: fix mem-leak

earlyConstructedSockets is a QObject, but had no parent and was never
deleted, leaking all the data is holds.

Fix by giving it a parent.

The code predates the begin of the public history.

Pick-to: 6.6 6.5 6.2 5.15
Change-Id: Ibc5688afd6111e84f591c37e39b6bb618d76c47a
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

tests/auto/network/socket/qtcpsocket/tst_qtcpsocket.cpp

@@ -281,7 +281,7 @@ tst_QTcpSocket::tst_QTcpSocket()
     tmpSocket = 0;
 
     //This code relates to the socketsConstructedBeforeEventLoop test case
-    earlyConstructedSockets = new SocketPair;
+    earlyConstructedSockets = new SocketPair(this);
     QVERIFY(earlyConstructedSockets->create());
     earlyBytesWrittenCount = 0;
     earlyReadyReadCount = 0;