Avoid transfers crossing a 4GB boundary, which can lead to data

corruption.  Thanks to scottl@ for the suggestion.

This change will likely be revised after consideration of a general
method to address this type of issue for other drivers.

Sponsored by:   Sandvine Incorporated
MFC after:      3 days

sys/dev/aac/aac_pci.c

@@ -403,7 +403,8 @@ aac_pci_attach(device_t dev)
 	 * Note that some of these controllers are 64-bit capable.
 	 */
 	if (bus_dma_tag_create(NULL, 			/* parent */
-			       PAGE_SIZE, 0,		/* algnmnt, boundary */
+			       PAGE_SIZE,		/* alignment */
+			       ((bus_size_t)((uint64_t)1 << 32)), /* boundary*/
 			       BUS_SPACE_MAXADDR,	/* lowaddr */
 			       BUS_SPACE_MAXADDR, 	/* highaddr */
 			       NULL, NULL, 		/* filter, filterarg */