nda: Fix comment

Fix a comment that was left over from the orignial
implementation. Explain how pending transactions in hardware are
completed/aborted in the SIM prior to ndacleanup being called.

Sponsored by:		Netflix

sys/cam/nvme/nvme_da.c

@@ -601,9 +601,10 @@ ndaoninvalidate(struct cam_periph *periph)
 #endif
 
 	/*
-	 * Return all queued I/O with ENXIO.
-	 * XXX Handle any transactions queued to the card
-	 *     with XPT_ABORT_CCB.
+	 * Return all queued I/O with ENXIO. Transactions may be queued up here
+	 * for retry (since we are called while there's other transactions
+	 * pending). Any requests in the hardware will drain before ndacleanup
+	 * is called.
 	 */
 	cam_iosched_flush(softc->cam_iosched, NULL, ENXIO);