Instead of creating it in NMSettings, where we must use
NM_IS_DEVICE_ETHERNET() (not NM_DEVICE_TYPE_ETHERNET because various generic
devices masquerade as NM_DEVICE_TYPE_ETHERNET too), push knowledge
of which device types create default wired connections into the device
types themselves. This solves a problem with testcases where
libNetworkManager.a (which testcases link to) requires the symbol
nm_type_device_ethernet().
Due to an error in the loop logic, if there were no connections yet (like
a fresh install or a livecd or whatever) no default name would be returned
and thus ethernet devices wouldn't come up automatically. Fix that loop
error and add testcases for it.