Description of problem:
S-C-Network fails to save new modem connections, "KeyError: 'Mtu'"

Version-Release number of selected component (if applicable):
system-config-network-1.5.1-1.fc9.noarch

How reproducible:
Always

Steps to Reproduce:
1.Launch S-C-Network
2.Create a new modem connection
3.Click File > Save
  
Actual results:
Component: system-config-network
Version: 1.5.1
Summary: TB4985ac49 NCDialup.py:158:save:KeyError: 'Mtu'

Traceback (most recent call last):
  File "/usr/share/system-config-network/netconfpkg/gui/maindialog.py", line
831, in on_applyButton_clicked
    self.save()
  File "/usr/share/system-config-network/netconfpkg/gui/maindialog.py", line
393, in save
    self.saveDevices()
  File "/usr/share/system-config-network/netconfpkg/gui/maindialog.py", line
413, in saveDevices
    devicelist.save()
  File "/usr/share/system-config-network/netconfpkg/NCDeviceList.py", line 228,
in save
    dev.save()
  File "/usr/share/system-config-network/netconfpkg/NCDevice.py", line 377, in save
    self.Dialup.save( conf )
  File "/usr/share/system-config-network/netconfpkg/NCDialup.py", line 585, in save
    Dialup.save(self, parentConf)
  File "/usr/share/system-config-network/netconfpkg/NCDialup.py", line 158, in save
    if self.__dict__[selfkey]:
KeyError: 'Mtu'

Local variables in innermost frame:
confkey: MTU
parentConf: <netconfpkg.NCDevice.ConfDevice instance at 0x90f75ac>
self: Dialup.StupidMode=True
Dialup.InitString=
Dialup.ProviderName=maxis3G
Dialup.DefRoute=True
Dialup.Authentication=+pap -chap
Dialup.Password=***
Dialup.PhoneNumber=*99#
Dialup.Login=maxis
Dialup.DialMode=manual
Dialup.Inherits=Modem0
Dialup.Areacode=
Dialup.Prefix=

selfkey: Mtu
conf: <netconfpkg.NCDevice.ConfDevice instance at 0x90f75ac>

Expected results:
Save successful

Additional info:

 - Attached a quick hack to ignore missing keys