bnxt_en: Reserve rings in bnxt_set_channels() if device is down.

The current code does not reserve rings during ethtool -L when the device
is down.  The rings will be reserved when the device is later opened.

Change it to reserve rings during ethtool -L when the device is down.
This provides a better guarantee that the device open will be successful
when the rings are reserved ahead of time.
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c

@@ -584,6 +584,8 @@ static int bnxt_set_channels(struct net_device *dev,
 			 * to renable
 			 */
 		}
+	} else {
+		rc = bnxt_reserve_rings(bp);
 	}
 
 	return rc;