app/testpmd: new commands for syn filter

Following commands of syn filter are removed:
  - add_syn_filter (port_id) priority (high|low) queue (queue_id)
  - remove_syn_filter (port_id)
  - get_syn_filter (port_id)
New command is added for syn filter by using filter_ctrl API and new
syn filter structure:
  - syn_filter (port_id) (add|del) priority (high|low) queue (queue_id)

Signed-off-by: Jingjing Wu <jingjing.wu@intel.com>