Add InvalidArgument error for Default Gateway

sdbusplus now supports errors on properties.

Change-Id: Ida480c5b161dcf2ab399c04904f34bee9f303a6c
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/xyz/openbmc_project/Network/SystemConfiguration.interface.yaml b/xyz/openbmc_project/Network/SystemConfiguration.interface.yaml
index 346f53e..a5bdd2f 100644
--- a/xyz/openbmc_project/Network/SystemConfiguration.interface.yaml
+++ b/xyz/openbmc_project/Network/SystemConfiguration.interface.yaml
@@ -9,3 +9,5 @@
       type: string
       description: >
           default gateway of the system.
+      errors:
+        - xyz.openbmc_project.Common.Error.InvalidArgument