The gateway is a global property of the IPv4/IPv6 configuration, not
an attribute of any particular address. So represent it as such in the
API; remove the gateway from NMIPAddress, and add it to
NMSettingIPConfig.
Behind the scenes, the gateway is still serialized along with the
first address in NMSettingIPConfig:addresses, and is deserialized from
that if the settings dictionary doesn't contain a 'gateway' key.
Adjust nmcli's interactive mode to prompt for IP addresses and gateway
separately. (Patch partly from Jirka Klimeš.)
Split a base NMSettingIPConfig class out of NMSettingIP4Config and
NMSettingIP6Config, and update things accordingly.
Further simplifications of now-redundant IPv4-vs-IPv6 code are
possible, and should happen in the future.
Add key-value attributes to NMIPAddress and NMIPRoute, and use them to
store IPv4 address labels. Demote NMSettingIP4Config:address-labels to
a D-Bus-only property, and arrange for :addresses setter to read the
labels out of that property when creating the addresses.
Merge NMIP4Address and NMIP6Address into NMIPAddress, and NMIP4Route
and NMIP6Route into NMIPRoute. The new types represent IP addresses as
strings, rather than in binary, and so are address-family agnostic.
