ethernet_interface: Normalize IP for gateway
ethernet_interface: Normalize IP for gateway

This makes sure gateways that are the same value but different string
representations are ignored.

Change-Id: I48cee3487276edce09ae2ee122d387d6a2a39d68
Signed-off-by: William A. Kennington III <30fff5198f4d10ca1117e5f3ec82f3b4b8900d81@google.com>

openbmc/phosphor-networkd,openbmc/phosphor-networkd