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

With commit d75b1ade ("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: d75b1ade ("net: less interrupt masking in NAPI")
Signed-off-by: NFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bcmsysport.c

@@ -731,9 +731,11 @@ static int bcm_sysport_tx_poll(struct napi_struct *napi, int budget)
 		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)