NetworkEdit: use pvetextfield instead of numberfield

because numberfield does not have 'deleteEmpty' functionality.

www/manager/Toolkit.js

@@ -31,6 +31,11 @@ Ext.apply(Ext.form.field.VTypes, {
     IP6CIDRAddressText:  gettext('Example') + ': 2001:DB8::42/64',
     IP6CIDRAddressMask:  /[A-Fa-f0-9:\/]/,
 
+    IP6PrefixLength:  function(v) {
+	return v >= 0 && v <= 128;
+    },
+    IP6PrefixLengthText:  gettext('Example') + ': X, where 0 <= X <= 128',
+    IP6PrefixLengthMask:  /[0-9]/,
     
     IP64Address:  function(v) {
         return IP64_match.test(v);

www/manager/node/NetworkEdit.js

@@ -242,13 +242,12 @@ Ext.define('PVE.node.NetworkEdit', {
 		    name: 'address6'
 		},
 		{
-		    xtype: 'numberfield',
+		    xtype: 'pvetextfield',
 		    deleteEmpty: !me.create,
 		    fieldLabel: gettext('Prefix length'),
+		    vtype: 'IP6PrefixLength',
 		    name: 'netmask6',
 		    value: '',
-		    minValue: 0,
-		    maxValue: 128,
 		    allowBlank: true,
 		    validator: function(value) {
 			/*jslint confusion: true */