igb: Fix not adding filter elements to the list

Because the order of the parameters passes to 'hlist_add_behind()' was
inverted, the 'parent' node was added "behind" the 'input', as input
is not in the list, this causes the 'input' node to be lost.

Fixes: 0e71def2 ("igb: add support of RX network flow classification")
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>