hv_netvsc: Fix unwanted rx_table reset

In existing code, the receive indirection table, rx_table, is in
struct rndis_device, which will be reset when changing MTU, ringparam,
etc. User configured receive indirection table values will be lost.

To fix this, move rx_table to struct net_device_context, and check
netif_is_rxfh_configured(), so rx_table will be set to default only
if no user configured value.

Fixes: ff4a4419

 ("netvsc: allow get/set of RSS indirection table")
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>