Alloc/free Pcap import options dialog every time

The earlier code was trying to reuse the dialog but this was throwing
an unexpected error every time -

    External WM_DESTROY received for QWidgetWindow

This commit fixes this error message

client/port.cpp

@@ -609,7 +609,6 @@ bool Port::openStreams(QString fileName, bool append, QString &error)
         int ret;
         optDialog->setParent(mainWindow, Qt::Dialog);
         ret = optDialog->exec();
-        optDialog->setParent(0, Qt::Dialog);
         if (ret == QDialog::Rejected)
             goto _user_opt_cancel;
     }

common/pcapfileformat.cpp

@@ -44,6 +44,7 @@ PcapImportOptionsDialog::PcapImportOptionsDialog(QVariantMap *options)
     : QDialog(NULL)
 {
     setupUi(this);
+    setAttribute(Qt::WA_DeleteOnClose);
     options_ = options;
 
     viaPdml->setChecked(options_->value("ViaPdml").toBool());
@@ -72,13 +73,10 @@ PcapFileFormat::PcapFileFormat()
     importOptions_.insert("ViaPdml", true);
     importOptions_.insert("RecalculateCksums", true);
     importOptions_.insert("DoDiff", true);
-
-    importDialog_ = NULL;
 }
 
 PcapFileFormat::~PcapFileFormat()
 {
-    delete importDialog_;
 }
 
 bool PcapFileFormat::open(const QString fileName,
@@ -709,10 +707,7 @@ _exit:
 
 QDialog* PcapFileFormat::openOptionsDialog()
 {
-    if (!importDialog_)
-        importDialog_ = new PcapImportOptionsDialog(&importOptions_);
-
-    return importDialog_;
+    return new PcapImportOptionsDialog(&importOptions_);
 }
 
 bool PcapFileFormat::isMyFileFormat(const QString /*fileName*/)

common/pcapfileformat.h

@@ -81,7 +81,6 @@ private:
 
     QDataStream fd_;
     QVariantMap importOptions_;
-    PcapImportOptionsDialog *importDialog_;
 };
 
 extern PcapFileFormat pcapFileFormat;

common/pcapfileimport.ui

@@ -7,7 +7,7 @@
     <x>0</x>
     <y>0</y>
     <width>326</width>
-    <height>112</height>
+    <height>132</height>
    </rect>
   </property>
   <property name="windowTitle">