net/mlx5e: fix build error without CONFIG_SYSFS

Commit 9008ae07 ("net/mlx5e: Minimize mlx5e_{open/close}_locked")
copied the calls to netif_set_real_num_{tx,rx}_queues from
mlx5e_open_locked to mlx5e_activate_priv_channels and wraps them in an
if condition to test for netdev->real_num_{tx,rx}_queues.

But netdev->real_num_rx_queues is conditionally compiled in if CONFIG_SYSFS
is set. Without CONFIG_SYSFS the build fails:

drivers/net/ethernet/mellanox/mlx5/core/en_main.c: In function 'mlx5e_activate_priv_channels':
drivers/net/ethernet/mellanox/mlx5/core/en_main.c:2515:12: error: 'struct net_device' has no member named 'real_num_rx_queues'; did you mean 'real_num_tx_queues'?

Fix this by unconditionally call netif_set_real_num{tx,rx}_queues like before
commit 9008ae07.

Fixes: 9008ae07 ("net/mlx5e: Minimize mlx5e_{open/close}_locked")
Signed-off-by: Tobias Regnery <tobias.regnery@gmail.com>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>