networks: Add more options for IPv6 configuration method

- If an existing network manager connection with the missing values is ever
edited, it leads an awkward interface.

- So, complete the setting by allowing values supported by Network Manager.

Tests:

- Create new connections with the new values 'link-local' and 'disabled'.
Connection creation succeeds.

- Editing connection to these values works too.

- When 'link-local' or 'disabled' values are selected, primary and secondary DNS
fields are disabled.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: Veiko Aasa <veiko17@disroot.org>

plinth/modules/networks/forms.py

@@ -107,10 +107,14 @@ class ConnectionForm(forms.Form):
             ('dhcp',
              _('Automatic (DHCP only): Configure automatically, use Internet '
                'connection from this network')),
+            ('link-local',
+             _('Link-local: Configure automatically to use an address that is '
+               'only relevant to this network.')),
             ('manual',
              _('Manual: Use manually specified parameters, use Internet '
                'connection from this network')),
             ('ignore', _('Ignore: Ignore this addressing method')),
+            ('disabled', _('Disabled: Disable IPv6 for this connection')),
         ])
     ipv6_address = forms.CharField(
         label=_('Address'), validators=[validators.validate_ipv6_address],

plinth/modules/networks/views.py

@@ -30,6 +30,8 @@ CONNECTION_METHOD_STRINGS = {
     'manual': gettext_lazy('manual'),
     'shared': gettext_lazy('shared'),
     'link-local': gettext_lazy('link-local'),
+    'dhcp': gettext_lazy('dhcp'),
+    'ignore': gettext_lazy('ignore'),
 }
 
 # i18n for device.state