Create the IPv6 AddressState Redfish node for OCP

The Open Compute Project defines the IPv6 AddressState entry to be a
mandatory field. OpenBMC does not have any support in phosphor-network
for reporting the actual IPv6 state. The AddressState field is allowed
to be null. This commit returns the AddressState as a null.

Tested:
Ran service validator
Ran a GET on Managers/bmc/EthernetInterfaces/eth0 and saw the addition
of the AddressState, and that it was null.

Change-Id: Ia2847f94ac73fc05ff2ca1be40a3f601fa0a3dfc
Signed-off-by: Johnathan Mantey <johnathanx.mantey@intel.com>
diff --git a/redfish-core/lib/ethernet.hpp b/redfish-core/lib/ethernet.hpp
index b32520b..d0c9a37 100644
--- a/redfish-core/lib/ethernet.hpp
+++ b/redfish-core/lib/ethernet.hpp
@@ -1849,13 +1849,15 @@
         {
             ipv6_array.push_back({{"Address", ipv6_config.address},
                                   {"PrefixLength", ipv6_config.prefixLength},
-                                  {"AddressOrigin", ipv6_config.origin}});
+                                  {"AddressOrigin", ipv6_config.origin},
+                                  {"AddressState", nullptr}});
             if (ipv6_config.origin == "Static")
             {
                 ipv6_static_array.push_back(
                     {{"Address", ipv6_config.address},
                      {"PrefixLength", ipv6_config.prefixLength},
-                     {"AddressOrigin", ipv6_config.origin}});
+                     {"AddressOrigin", ipv6_config.origin},
+                     {"AddressState", nullptr}});
             }
         }
     }