hyperv: Add buffer for extended info after the RNDIS response message.

In some response messages, there may be some extended info after the
message.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>