rtnetlink_server: Refresh for route changes
rtnetlink_server: Refresh for route changes

We want to make sure we update the DefaultGateway if it changes.
Otherwise when someone changes our gateway we don't update the state of
the phosphor-network daemon.

Tested:
    Editted the default route manually through netlink and saw the
    update get picked up in the dbus interface.

Change-Id: Ib4f5bafbdb7615e235f47bc8fa372396491e69e6
Signed-off-by: William A. Kennington III <30fff5198f4d10ca1117e5f3ec82f3b4b8900d81@google.com>

openbmc/phosphor-networkd,openbmc/phosphor-networkd