Network: Modify Nameservers Property to include NotAllowed Error

As per the below commit, Setting the Static Nameservers is
restricted while in DHCP mode.
- https://gerrit.openbmc-project.xyz/#/c/openbmc/phosphor-networkd/+/24224/

The idea of this commit is to modify the property to handle
the NotAllowed Error.

Change-Id: I6570230127e817ce9cab3f8b817aedfbe0b68c57
Signed-off-by: Manojkiran Eda <manojkiran.eda@gmail.com>
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/xyz/openbmc_project/Network/EthernetInterface.interface.yaml b/xyz/openbmc_project/Network/EthernetInterface.interface.yaml
index 8363505..c553014 100644
--- a/xyz/openbmc_project/Network/EthernetInterface.interface.yaml
+++ b/xyz/openbmc_project/Network/EthernetInterface.interface.yaml
@@ -32,6 +32,7 @@
           DNS servers on the interface.
       errors:
           - xyz.openbmc_project.Common.Error.InvalidArgument
+          - xyz::openbmc_project.Common.Error.NotAllowed
     - name: NTPServers
       type: array[string]
       description: >