hv_netvsc: Rearrange the hv_negtvsc_packet to be space efficient

Rearrange the elements of struct hv_negtvsc_packet for optimal layout -
eliminate unnecessary padding.

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>