Update the error on deleting a link local address

It is in reference to https://github.com/openbmc/openbmc/issues/2342

Currently, when a user tries to delete a non-static ip address,
it throws an error as "the operation failed internally"

With the update, when an attempt is made to delete the link-local
address of the bmc it throws "The operation is not allowed" error

Tested by:

Current behaviour:

busctl call xyz.openbmc_project.Network
/xyz/openbmc_project/network/eth1/_66e80_3a_3aa94...
xyz.openbmc_project.Object.Delete Delete

response: Call failed: The operation failed internally.

Modified behaviour:

busctl call xyz.openbmc_project.Network
/xyz/openbmc_project/network/eth1/_66e80_3a_3aa94...
xyz.openbmc_project.Object.Delete Delete

response: Call failed: The operation is not allowed

Change-Id: Ib5df33b8ad356a868aecc508ad6531ed15390a1d
Signed-off-by: Jishnu CM <jishnunambiarcm@duck.com>
diff --git a/src/ipaddress.cpp b/src/ipaddress.cpp
index e678725..189c3bf 100644
--- a/src/ipaddress.cpp
+++ b/src/ipaddress.cpp
@@ -95,7 +95,8 @@
                    "{NET_PFX} interface {NET_INTF}",
                    "NET_IP", address(), "NET_PFX", prefixLength(), "NET_INTF",
                    parent.get().interfaceName());
-        elog<InternalFailure>();
+
+        elog<NotAllowed>(Reason("Not allowed to delete a non-static address"));
     }
 
     std::unique_ptr<IPAddress> ptr;