net: sched: provide shim definitions for taprio_offload_{get,free}

All callers of taprio_offload_get() and taprio_offload_free() prior to
the blamed commit are conditionally compiled based on CONFIG_NET_SCH_TAPRIO.

felix_vsc9959.c is different; it provides vsc9959_qos_port_tas_set()
even when taprio is compiled out.

Provide shim definitions for the functions exported by taprio so that
felix_vsc9959.c is able to compile. vsc9959_qos_port_tas_set() in that
case is dead code anyway, and ocelot_port->taprio remains NULL, which is
fine for the rest of the logic.

Fixes: 1c9017e44a ("net: dsa: felix: keep reference on entire tc-taprio config")
Reported-by: Colin Foster <colin.foster@in-advantage.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Colin Foster <colin.foster@in-advantage.com>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Link: https://lore.kernel.org/r/20220704190241.1288847-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/pkt_sched.h

@@ -173,11 +173,28 @@ struct tc_taprio_qopt_offload {
 	struct tc_taprio_sched_entry entries[];
 };
 
+#if IS_ENABLED(CONFIG_NET_SCH_TAPRIO)
+
 /* Reference counting */
 struct tc_taprio_qopt_offload *taprio_offload_get(struct tc_taprio_qopt_offload
 						  *offload);
 void taprio_offload_free(struct tc_taprio_qopt_offload *offload);
 
+#else
+
+/* Reference counting */
+static inline struct tc_taprio_qopt_offload *
+taprio_offload_get(struct tc_taprio_qopt_offload *offload)
+{
+	return NULL;
+}
+
+static inline void taprio_offload_free(struct tc_taprio_qopt_offload *offload)
+{
+}
+
+#endif
+
 /* Ensure skb_mstamp_ns, which might have been populated with the txtime, is
  * not mistaken for a software timestamp, because this will otherwise prevent
  * the dispatch of hardware timestamps to the socket.