fm10k: Fix handling of NAPI budget when multiple queues are enabled per vector

BugLink: http://bugs.launchpad.net/bugs/1536475

This patch corrects an issue in which the polling routine would increase
the budget for Rx to at least 1 per queue if multiple queues were present.
This would result in Rx packets being processed when the budget was 0 which
is meant to indicate that no Rx can be handled.
Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Tested-by: Krishneil Singh <Krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit 9f872986)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/net/ethernet/intel/fm10k/fm10k_main.c

@@ -1428,6 +1428,10 @@ static int fm10k_poll(struct napi_struct *napi, int budget)
 	fm10k_for_each_ring(ring, q_vector->tx)
 		clean_complete &= fm10k_clean_tx_irq(q_vector, ring);
 
+	/* Handle case where we are called by netpoll with a budget of 0 */
+	if (budget <= 0)
+		return budget;
+
 	/* attempt to distribute budget to each queue fairly, but don't
 	 * allow the budget to go below 1 because we'll exit polling
 	 */