IPv4/IPv6 Gateway: Configure GatewayOnLink

Currently when both interfaces configured static ip addresses and one of
that static ip address is in private network then while reload network
configuration further, route order keep changes and interface with
private network is not reachable when other gateway route is on the top
of routing table.

This commit configures IPv4/IPv6 static gateway using systemd-networkd's
Route option and sets GatewayOnLink option and make sure interfaces
network reachable irrespective of route order while reloading networkd.

Tested By:
configure one interface in static and other interface DHCP.
configure both interfaces with static IP and one interface on private
network.

Sample IPv4 network route added in systemd-networkd configuration file
[Route]
GatewayOnLink=true
Gateway=9.10.x.1

Change-Id: Id7c9ba74cf7e71e6105536c5affc905754cae908
Signed-off-by: Ravi Teja <raviteja28031990@gmail.com>
1 file changed