Add IPv4/Ipv6 default gateway properties on Ethernet interface

Currently, OpenBMC stack allows a single default gateway
for the system(default gateway property present in system config)
Latest kernel allows to configure multiple default gateways.
so its proposed OpenBMC D-bus interfaces to tie the gateway property
with the Ethernet interface schema instead of system configuration dbus
interfaces and discussed over OpenBmc mailing list.

Clients will be able to configure default gateway for each Ethernet interface.
clients will use dbus property on Ethernet interface instead of system config
interface.

Implementation:
https://gerrit.openbmc-project.xyz/c/openbmc/phosphor-networkd/+/34852

Signed-off-by: Ravi Teja <raviteja28031990@gmail.com>
Change-Id: I5d671cac5ec8ef4ccd8deac0c0626e8d52db70eb
diff --git a/xyz/openbmc_project/Network/SystemConfiguration.interface.yaml b/xyz/openbmc_project/Network/SystemConfiguration.interface.yaml
index 917a5d6..29033fb 100644
--- a/xyz/openbmc_project/Network/SystemConfiguration.interface.yaml
+++ b/xyz/openbmc_project/Network/SystemConfiguration.interface.yaml
@@ -5,6 +5,9 @@
       type: string
       description: >
           The value of this property shall be host name of the system.
+    # Deprecating these "DefautGateway" and "DefaultGateway6" properties.
+    # These are no longer needed, as we are going to support Default gateway
+    # per Ethernet interface.
     - name: DefaultGateway
       type: string
       description: >