ixgbe: fix build err, num_rx_queues is only available with CONFIG_RPS

In the recent support for layer 2 hardware acceleration, I added a
few references to real_num_rx_queues and num_rx_queues which are
only available with CONFIG_RPS.

The fix is first to remove unnecessary references to num_rx_queues.
Because the hardware offload case is limited to cases where RX queues
and TX queues are equal we only need a single check. Then wrap the
single case in an ifdef.

The patch that introduce this is here,

commit a6cc0cfa


Author: John Fastabend <john.r.fastabend@intel.com>
Date:   Wed Nov 6 09:54:46 2013 -0800

    net: Add layer 2 hardware acceleration operations for macvlan devices

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>