fm10k: clarify action when updating the VLAN table

Clarify the comment for when entering promiscuous mode that we update
the VLAN table. Add a comment distinguishing the case where we're
exiting promiscuous mode and need to clear the entire VLAN table.

Signed-off-by: Ngai-Mint Kwan <ngai-mint.kwan@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@gmail.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/fm10k/fm10k_netdev.c

@@ -1165,10 +1165,12 @@ static void fm10k_set_rx_mode(struct net_device *dev)
 
 	/* update xcast mode first, but only if it changed */
 	if (interface->xcast_mode != xcast_mode) {
-		/* update VLAN table */
+		/* update VLAN table when entering promiscuous mode */
 		if (xcast_mode == FM10K_XCAST_MODE_PROMISC)
 			fm10k_queue_vlan_request(interface, FM10K_VLAN_ALL,
 						 0, true);
+
+		/* clear VLAN table when exiting promiscuous mode */
 		if (interface->xcast_mode == FM10K_XCAST_MODE_PROMISC)
 			fm10k_clear_unused_vlans(interface);