The code flow is actually somewhat simpler this way since the
subclasses don't have to ask NMDeviceWired for the address
every time. Plus then NMDeviceWired doesn't have to know
anything about its subclasses in the constructor.
When no slave is present, dynamic IP configuration (DHCPv4, DHCPv6,
IPv6 autoconf) cannot proceed. But static and link-local
configuration can. So if IPv4 requires DHCP but IPv6 is static,
it makes no sense to block IPv6 configuration from proceeding
just because DHCPv4 cannot.
Rather than having NMDevice subclasses connect to their own
::state-changed signal, fix up the signal definition so they can just
override the class handler.
The idea was copied from gtk, but it's only used there in cases where
the method's wrapper function and default implementation would
otherwise have the same name, which never happens in NM because our
method implementations aren't prefixed with the type name, so it's
just noise here.
There's no way to specify the MAC address bond interfaces have
since they take the MAC address of their slaves, so NMDeviceBond
doesn't implement hwaddr_matches(). This check would always
return FALSE, and thus we'd never match.
