Qt4: define generic font-family instead font in net-open helper-text

modules/gui/qt4/ui/open_net.ui

@@ -50,7 +50,7 @@
          <string>&lt;!DOCTYPE HTML PUBLIC &quot;-//W3C//DTD HTML 4.0//EN&quot; &quot;http://www.w3.org/TR/REC-html40/strict.dtd&quot;&gt;
 &lt;html&gt;&lt;head&gt;&lt;meta name=&quot;qrichtext&quot; content=&quot;1&quot; /&gt;&lt;style type=&quot;text/css&quot;&gt;
 p, li { white-space: pre-wrap; }
-&lt;/style&gt;&lt;/head&gt;&lt;body style=&quot; font-family:'DejaVu Sans'; font-size:8pt; font-weight:400; font-style:normal;&quot;&gt;
+&lt;/style&gt;&lt;/head&gt;&lt;body style=&quot; font-family:'sans'; font-size:8pt; font-weight:400; font-style:normal;&quot;&gt;
 &lt;p style=&quot; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;&quot;&gt;&lt;span style=&quot; color:#838383;&quot;&gt;http://www.example.com/stream.avi&lt;/span&gt;&lt;/p&gt;
 &lt;p style=&quot; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;&quot;&gt;&lt;span style=&quot; color:#838383;&quot;&gt;rtp://@1234&lt;/span&gt;&lt;/p&gt;
 &lt;p style=&quot; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;&quot;&gt;&lt;span style=&quot; color:#838383;&quot;&gt;mms://mms.examples.com/stream.asx&lt;/span&gt;&lt;/p&gt;