hv_netvsc: make recording RSS hash depend on feature flag

The recording of RSS hash should be controlled by NETIF_F_RXHASH.

Fixes: 1fac7ca4

 ("hv_netvsc: record hardware hash in skb")
Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>