cxgb4: when disabling dcb set txq dcb priority to 0

BugLink: https://bugs.launchpad.net/bugs/1792377

[ Upstream commit 5ce36338 ]

When we are disabling DCB, store "0" in txq->dcb_prio
since that's used for future TX Work Request "OVLAN_IDX"
values. Setting non zero priority upon disabling DCB
would halt the traffic.
Reported-by: AMG Zollner Robert <robert@cloudmedia.eu>
CC: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: Casey Leedom <leedom@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c

@@ -338,7 +338,7 @@ static void dcb_tx_queue_prio_enable(struct net_device *dev, int enable)
 				"Can't %s DCB Priority on port %d, TX Queue %d: err=%d\n",
 				enable ? "set" : "unset", pi->port_id, i, -err);
 		else
-			txq->dcb_prio = value;
+			txq->dcb_prio = enable ? value : 0;
 	}
 }
 #endif /* CONFIG_CHELSIO_T4_DCB */