net: bql: fix building with BQL disabled

It is now possible to disable BQL, but that causes the cpsw driver to break:

drivers/net/ethernet/ti/am65-cpsw-nuss.c:297:28: error: no member named 'dql' in 'struct netdev_queue'
  297 |                    dql_avail(&netif_txq->dql),

There is already a helper function in net/sch_generic.h that could
be used to help here. Move its implementation into the common
linux/netdevice.h along with the other bql interfaces and change
both users over to the new interface.

Fixes: ea7f3cf ("net: bql: allow the config to be disabled")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/am65-cpsw-nuss.c

@@ -294,7 +294,7 @@ static void am65_cpsw_nuss_ndo_host_tx_timeout(struct net_device *ndev,
 		   txqueue,
 		   netif_tx_queue_stopped(netif_txq),
 		   jiffies_to_msecs(jiffies - trans_start),
-		   dql_avail(&netif_txq->dql),
+		   netdev_queue_dql_avail(netif_txq),
 		   k3_cppi_desc_pool_avail(tx_chn->desc_pool));
 
 	if (netif_tx_queue_stopped(netif_txq)) {

include/linux/netdevice.h

@@ -3499,6 +3499,16 @@ static inline void netdev_queue_set_dql_min_limit(struct netdev_queue *dev_queue
 #endif
 }
 
+static inline int netdev_queue_dql_avail(const struct netdev_queue *txq)
+{
+#ifdef CONFIG_BQL
+	/* Non-BQL migrated drivers will return 0, too. */
+	return dql_avail(&txq->dql);
+#else
+	return 0;
+#endif
+}
+
 /**
  *	netdev_txq_bql_enqueue_prefetchw - prefetch bql data for write
  *	@dev_queue: pointer to transmit queue

include/net/sch_generic.h

@@ -238,12 +238,7 @@ static inline bool qdisc_may_bulk(const struct Qdisc *qdisc)
 
 static inline int qdisc_avail_bulklimit(const struct netdev_queue *txq)
 {
-#ifdef CONFIG_BQL
-	/* Non-BQL migrated drivers will return 0, too. */
-	return dql_avail(&txq->dql);
-#else
-	return 0;
-#endif
+	return netdev_queue_dql_avail(txq);
 }
 
 struct Qdisc_class_ops {