Fix inputMask for IGMPv3 source IP

The old mask 009.009.009.009 does not compute to valid for input 1.2.3.4
and the Qt delegate doesn't accept it with Qt5 (not the case with Qt4)

Although the new mask 000.000.000.000 cannot prevent invalid entries
like 1.2.. or 300.400.500.600, I decided it was better to accept invalid
input (which gets converted to 0.0.0.0) instead of unintentionally not
allowing valid entries.

Fixes #292

common/ipv4addressdelegate.h

@@ -50,7 +50,7 @@ inline QWidget* IPv4AddressDelegate::createEditor(QWidget *parent,
     ipEdit = static_cast<QLineEdit*>(QItemDelegate::createEditor(
                 parent, option, index));
 
-    ipEdit->setInputMask("009.009.009.009;"); // FIXME: use validator
+    ipEdit->setInputMask("000.000.000.000;"); // FIXME: use validator
 
     return ipEdit;
 }