Always allow Ethernet to be an upstream

If there are any upstream types defined at all, make sure that
either TYPE_ETHERNET is included somewhere within the sorted list
or force it to be at the front.

Test: as follows
    - built
    - flashed
    - booted
    - runtest frameworks-net passes
Bug: 32163131
Bug: 36076442
Change-Id: Ie61d1358f73d518de23f6ca48ca2765ca14a1067