settings: create default wired connection from NMDeviceEthernet

settings: create default wired connection from NMDeviceEthernet

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().