Identify Ethernet interfaces in check_ethernet.hook.

BUG=chromium-os:35478
TEST=Tested check_ethernet.hook on machines with the following settings:
1. with an Ethernet interface
2. with two Ethernet interfaces
3. with an Ethernet interface and an E362 modem.

Change-Id: I57de4e50e9ceb73141e240bfc2219432b9d8d11a
Reviewed-on: https://gerrit.chromium.org/gerrit/36439
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Ready: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/37485
Tested-by: Chris Sosa <sosa@chromium.org>
1 file changed