network: Don't save hidden configuration options

When switching from a particular IPv4 or IPv6 "addresses" method to
another, make sure that "address", "DNS" and "routes" are applied or
ignored depending on that method's capabilities.

For example, when switching from manual to automatic IPv4 "addresses"
method, we need to make sure that the old IP address, gateway, etc.
aren't actually used in the new setting.

https://bugzilla.gnome.org/show_bug.cgi?id=734337