Let only Ethernet manage ethernet interface up and down

When LAN link is changed for using ethernet interface from Ethernet tethering to Ethernet,
there is confiict as Ethernet Tethering is trying to make ethernet link down and Ethernet is trying to make ethernet link up.

So, this would make Ethernet only manage ethernet interface link state.

Test: manual
Bug: 130840861
Change-Id: I1cd40ae764bdeecbb59e3889e9399b7f4b05f9cc