[zephyr] Fixed GetNetworkInterfaces method (project-chip#37707)

GetNetworkInterfaces method does not set next pointer for the
specific interfaces. Because of that, it is not possible to
iterate through the elements returned by this method.

Author: kkasperczyk-no

src/platform/Zephyr/DiagnosticDataProviderImpl.cpp

@@ -369,6 +369,7 @@ CHIP_ERROR DiagnosticDataProviderImpl::GetNetworkInterfaces(NetworkInterface **
         }
 
         ifp->IPv6Addresses = chip::app::DataModel::List<chip::ByteSpan>(ifp->Ipv6AddressSpans, ipv6AddressesCount);
+        ifp->Next          = head;
         head               = ifp;
     }