ethernet_interface: Clean up object creation
ethernet_interface: Clean up object creation

This cleans up the loop and makes sure the interface parsing code
updates the local variables for each iteration of the loop.

Tested:
    Built and verified that objects were still being created as
    expected.

Change-Id: I5ba442538f6d2b5a4dc6a8a1261777c0303818d1
Signed-off-by: William A. Kennington III <30fff5198f4d10ca1117e5f3ec82f3b4b8900d81@google.com>

openbmc/phosphor-networkd,openbmc/phosphor-networkd