net: sched: fix typo in net_device ifdef

This should have been #ifdef not #if.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Fixes: d2788d34 ("net: sched: further simplify handle_ing")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>