enable eth0 by default with highest priority, monitor ethenet state changes

[jimsmt]

Tested several devices with and without Ethernet, need more tests

[flyrouter]

Thank you very much for your work
I think our colleagues
@widgetii @cronyx @p0i5k @viktorxda @ZigFisher @themactep @ialexlog @gtxaspec @dimerr
will consider and check your proposal and give feedback in the near future.

[flyrouter]

Since this PR is important, interesting and at the same time critical, preliminary experiments have been submitted to the Sandbox - https://github.com/OpenIPC/sandbox/tree/main/scripts/network

After passing all tests, edits and collecting feedback, a new PR will be created in the Firmware repository.

Thank you, @johndi3