Declare support for Ethernet if the service is running.

On some devices, support for TYPE_ETHERNET is not specified in
the networkAttributes config resource, even though the device is
capable of supporting Ethernet (e.g., via USB host adapters).
This leads to Ethernet working but various connectivity APIs
behaving as if it was not - for example, no CONNECTIVITY_ACTION
broadcasts will be issues when it connects or disconnects.

Ensure that ConnectivityService always treats Ethernet as
available if the service is running. Currently the service is
started if the device supports FEATURE_ETHERNET or
FEATURE_USB_HOST.

Bug: 37359230
Test: bullhead builds, boots
Test: ConnectivityServiceTest passes
Test: Ethernet is available even if removed from networkAttributes resource
Test: ConnectivityManagerTest CTS test passes
Change-Id: I58801bf4f0bbdc3ff6345ec6bfdc911ce045c8ab