hv_netvsc: Eliminate rndis_msg pointer from hv_netvsc_packet structure

Eliminate rndis_msg pointer from hv_netvsc_packet structure.

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