storvsc: use storage protocol version to determine storage capabilities

Use storage protocol version instead of vmbus protocol
version when determining storage capabilities.

Tested-by: Alex Ng <alexng@microsoft.com>
Signed-off-by: Keith Mange <keith.mange@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>