I/OAT: set tcp_dma_copybreak to 256k for I/OAT ver.3

Upcoming server platforms from Intel based on the Nehalem performance
have significantly improved CPU based copy performance.
However, the DMA engine can still be effective at higher I/O sizes
for TCP traffic and at this time copybreak
should be set to 256k for TCP traffic only.

Signed-off-by: Maciej Sosnowski <[e-mail]>
Signed-off-by: Shannon Nelson <[e-mail]>
Acked-by: Jeff Kirsher <[e-mail]>
Signed-off-by: Dan Williams <[e-mail]>

drivers/dma/ioatdma.h

···
 	#ifdef CONFIG_NET_DMA
 	switch (dev->version) {
 	case IOAT_VER_1_2:
-	case IOAT_VER_3_0:
 		sysctl_tcp_dma_copybreak = 4096;
 		break;
 	case IOAT_VER_2_0:
 		sysctl_tcp_dma_copybreak = 2048;
+		break;
+	case IOAT_VER_3_0:
+		sysctl_tcp_dma_copybreak = 262144;
 		break;
 	}
 	#endif