stm32/modnetwork: Change base entry of NIC object from type to base.

mod_network_nic_type_t doesn't need to be an actual uPy type, it just needs
to be an object.

ports/stm32/modnetwork.h

@@ -40,7 +40,7 @@
 struct netif;
 
 typedef struct _mod_network_nic_type_t {
-    mp_obj_type_t base;
+    mp_obj_base_t base;
     void (*poll_callback)(void *data, struct netif *netif);
 } mod_network_nic_type_t;
 
@@ -84,11 +84,11 @@ typedef struct _mod_network_socket_obj_t {
     };
 } mod_network_socket_obj_t;
 
-#endif
-
 extern const mod_network_nic_type_t mod_network_nic_type_wiznet5k;
 extern const mod_network_nic_type_t mod_network_nic_type_cc3k;
 
+#endif
+
 void mod_network_init(void);
 void mod_network_deinit(void);
 void mod_network_register_nic(mp_obj_t nic);