dpaa2: Perform bus_dma pre-write sync before enqueue operation

Without a proper synchronization payload of the egress TCP segments
can be corrupted as tuexen@ described in
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=292006#c31.

This patch is indirectly related to 292006 because a properly enabled
and announced support for the TX checksum offloading hides potentially
corrupted frame payload.

PR:		292006
Reported by:	tuexen@
Reviewed by:	...
Tested by:	dsl@
Differential Revision:	<https://reviews.freebsd.org/D###>
MFC after:	3 days

sys/dev/dpaa2/dpaa2_ni.c

@@ -3004,6 +3004,9 @@ dpaa2_ni_tx(struct dpaa2_ni_softc *sc, struct dpaa2_channel *ch,
 		goto err_unload;
 	}
 
+	bus_dmamap_sync(buf->dmat, buf->dmap, BUS_DMASYNC_PREWRITE);
+	bus_dmamap_sync(sgt->dmat, sgt->dmap, BUS_DMASYNC_PREWRITE);
+
 	/* TODO: Enqueue several frames in a single command */
 	for (int i = 0; i < DPAA2_NI_ENQUEUE_RETRIES; i++) {
 		/* TODO: Return error codes instead of # of frames */
@@ -3013,9 +3016,6 @@ dpaa2_ni_tx(struct dpaa2_ni_softc *sc, struct dpaa2_channel *ch,
 		}
 	}
 
-	bus_dmamap_sync(buf->dmat, buf->dmap, BUS_DMASYNC_PREWRITE);
-	bus_dmamap_sync(sgt->dmat, sgt->dmap, BUS_DMASYNC_PREWRITE);
-
 	if (rc != 1) {
 		fq->chan->tx_dropped++;
 		if_inc_counter(sc->ifp, IFCOUNTER_OERRORS, 1);