netvsc: don't access netdev->num_rx_queues directly

This structure member is hidden behind CONFIG_SYSFS, and we
get a build error when that is disabled:

drivers/net/hyperv/netvsc_drv.c: In function 'netvsc_set_channels':
drivers/net/hyperv/netvsc_drv.c:754:49: error: 'struct net_device' has no member named 'num_rx_queues'; did you mean 'num_tx_queues'?
drivers/net/hyperv/netvsc_drv.c: In function 'netvsc_set_rxfh':
drivers/net/hyperv/netvsc_drv.c:1181:25: error: 'struct net_device' has no member named 'num_rx_queues'; did you mean 'num_tx_queues'?

As the value is only set once to the argument of alloc_netdev_mq(),
we can compare against that constant directly.

Fixes: ff4a4419 ("netvsc: allow get/set of RSS indirection table")
Fixes: 2b01888d ("netvsc: allow more flexible setting of number of channels")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>