net: systemport: fix tx work done in TX napi poll

With commit d75b1ade567 ("net: less interrupt masking in NAPI") napi
repoll is done only when work_done == budget. bcm_sysport_tx_poll()
always returns 0 whether or not we completed the poll quantum.

Fix this by returning either 0 when we did complete the TX ring reclaim,
or budget to trigger a repoll.

Fixes: d75b1ade567 ("net: less interrupt masking in NAPI")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/broadcom/bcmsysport.c b/drivers/net/ethernet/broadcom/bcmsysport.c
index 531bb7c..3cb2411 100644
--- a/drivers/net/ethernet/broadcom/bcmsysport.c
+++ b/drivers/net/ethernet/broadcom/bcmsysport.c
@@ -731,9 +731,11 @@
 		napi_complete(napi);
 		/* re-enable TX interrupt */
 		intrl2_1_mask_clear(ring->priv, BIT(ring->index));
+
+		return 0;
 	}
 
-	return 0;
+	return budget;
 }
 
 static void bcm_sysport_tx_reclaim_all(struct bcm_sysport_priv *priv)