network: Fix changing addressing method (GH #307)
network: Fix changing addressing method (GH #307)

When changing the addressing method from manual to automatic, the IP
addresses where removed from connection object without removing the
Gateway property.  This causes a networkmanager error.

Create new SettingIP4Config object to avoid the need to reset all
propertys when changing methods

vignanl/Plinth,kkampardi/Plinth,jvalleroy/plinth-debian,harry-7/Plinth,vignanl/Plinth,jvalleroy/plinth-debian,freedomboxtwh/Plinth,jvalleroy/plinth-debian,kkampardi/Plinth,kkampardi/Plinth,vignanl/Plinth,jvalleroy/plinth-debian,freedomboxtwh/Plinth,harry-7/Plinth,kkampardi/Plinth,harry-7/Plinth,freedomboxtwh/Plinth,harry-7/Plinth,harry-7/Plinth,kkampardi/Plinth,vignanl/Plinth,freedomboxtwh/Plinth,jvalleroy/plinth-debian,freedomboxtwh/Plinth,vignanl/Plinth