QtNetwork: fix GCC 7 warnings

GCC 7 warns about implicit fall-throughs now.

Fix by adding the missing Q_FALLTHROUGH(), and, in one case, by
moving the existing suppressant into the correct position.

Change-Id: I7383f47e690b6334ef69c9df745c2205247ca7d0
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

src/network/access/qhttpnetworkconnectionchannel.cpp

@@ -1080,8 +1080,8 @@ void QHttpNetworkConnectionChannel::_q_encrypted()
                                       "detected unknown Next Protocol Negotiation protocol");
                 break;
             }
-            Q_FALLTHROUGH();
         }
+            Q_FALLTHROUGH();
         case QSslConfiguration::NextProtocolNegotiationNone:
             protocolHandler.reset(new QHttpProtocolHandler(this));
             connection->setConnectionType(QHttpNetworkConnection::ConnectionTypeHTTP);

src/network/kernel/qhostaddress.cpp

@@ -291,21 +291,27 @@ bool QNetmaskAddress::setAddress(const QHostAddress &address)
             d->clear();
             return false;       // invalid IP-style netmask
 
-            // the rest always falls through
         case 254:
             ++netmask;
+            Q_FALLTHROUGH();
         case 252:
             ++netmask;
+            Q_FALLTHROUGH();
         case 248:
             ++netmask;
+            Q_FALLTHROUGH();
         case 240:
             ++netmask;
+            Q_FALLTHROUGH();
         case 224:
             ++netmask;
+            Q_FALLTHROUGH();
         case 192:
             ++netmask;
+            Q_FALLTHROUGH();
         case 128:
             ++netmask;
+            Q_FALLTHROUGH();
         case 0:
             break;
         }