Extend the "ethernet.cloned-mac-address" and "wifi.cloned-mac-address"
settings. Instead of specifying an explicit MAC address, the additional
special values "permanent", "preserve", "random", "random-bia", "stable" and
"stable-bia" are supported.

"permanent" means to use the permanent hardware address. Previously that
was the default if no explict cloned-mac-address was set. The default is
thus still "permanent", but it can be overwritten by global
configuration.

"preserve" means not to configure the MAC address when activating the
device. That was actually the default behavior before introducing MAC
address handling with commit 1b49f941.

"random" and "random-bia" use a randomized MAC address for each
connection. "stable" and "stable-bia" use a generated, stable
address based on some token. The "bia" suffix says to generate a
burned-in address. The stable method by default uses as token the
connection UUID, but the token can be explicitly choosen via
"stable:<TOKEN>" and "stable-bia:<TOKEN>".

On a D-Bus level, the "cloned-mac-address" is a bytestring and thus
cannot express the new forms. It is replaced by the new
"assigned-mac-address" field. For the GObject property, libnm's API,
nmcli, keyfile, etc. the old name "cloned-mac-address" is still used.
Deprecating the old field seems more complicated then just extending
the use of the existing "cloned-mac-address" field, although the name
doesn't match well with the extended meaning.

There is some overlap with the "wifi.mac-address-randomization" setting.

https://bugzilla.gnome.org/show_bug.cgi?id=705545
https://bugzilla.gnome.org/show_bug.cgi?id=708820
https://bugzilla.gnome.org/show_bug.cgi?id=758301