Initialize the senderPort member variable in QIpPacketHeader

Address the "A constructor must initialize all data members of the
class" warning found by an Axivion scan.

Just as the destinationPort is defaulted to 0 initialize the senderPort
to be 0 as well.

Task-number: QTBUG-125026
Pick-to: 6.7 6.5
Change-Id: Ifec55ba4b6c23a6feed2b4816d4ba6aae061f1cd
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
(cherry picked from commit 213127a013b6ecafb36eae1014d5988198736712)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/network/kernel/qnetworkdatagram_p.h

@@ -25,6 +25,7 @@ class QIpPacketHeader
 public:
     QIpPacketHeader(const QHostAddress &dstAddr = QHostAddress(), quint16 port = 0)
         : destinationAddress(dstAddr), ifindex(0), hopLimit(-1), streamNumber(-1),
+          senderPort(0),
           destinationPort(port), endOfRecord(false)
     {}