i40e: update comment explaining where FDIR buffers are freed

The original comment implies that the only location where the raw_packet
buffer will be freed is in i40e_clean_tx_ring() which is incorrect. In
fact this isn't even the normal case. Update the comment explaining
where the memory is freed.

Change-ID: Ie0defc35ed1c3af183f81fdc60b6d783707a5595
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_txrx.c

@@ -432,7 +432,12 @@ unsupported_flow:
 		ret = -EINVAL;
 	}
 
-	/* The buffer allocated here is freed by the i40e_clean_tx_ring() */
+	/* The buffer allocated here will be normally be freed by
+	 * i40e_clean_fdir_tx_irq() as it reclaims resources after transmit
+	 * completion. In the event of an error adding the buffer to the FDIR
+	 * ring, it will immediately be freed. It may also be freed by
+	 * i40e_clean_tx_ring() when closing the VSI.
+	 */
 	return ret;
 }