hyperv: Adjust the size of sendbuf region to support ws2008r2

WS2008R2 is a supported platform and it turns out that the maximum sendbuf
size that ws2008R2 can support is only 15MB. Make the necessary
adjustment.
Signed-off-by: NK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/hyperv/hyperv_net.h

@@ -585,7 +585,7 @@ struct nvsp_message {
 
 #define NETVSC_RECEIVE_BUFFER_SIZE		(1024*1024*16)	/* 16MB */
 #define NETVSC_RECEIVE_BUFFER_SIZE_LEGACY	(1024*1024*15)  /* 15MB */
-#define NETVSC_SEND_BUFFER_SIZE			(1024 * 1024 * 16)   /* 16MB */
+#define NETVSC_SEND_BUFFER_SIZE			(1024 * 1024 * 15)   /* 15MB */
 #define NETVSC_INVALID_INDEX			-1