planning: adjust speed limit to 25 mph.

modules/planning/conf/planning.conf

 --flagfile=/apollo/modules/common/data/global_flagfile.txt
 --traffic_rule_config_filename=/apollo/modules/planning/conf/traffic_rule_config.pb.txt
 --nouse_cyber_time
---planning_upper_speed_limit=15.65
+--planning_upper_speed_limit=11.18
 --ignore_overlapped_obstacle=true
 --prioritize_change_lane
 --enable_reference_line_stitching
@@ -24,7 +24,7 @@
 # --default_qp_smoothing_eps_iter_ref=1e-3
 # --default_qp_smoothing_eps_num=-1e-3
 # --default_qp_smoothing_eps_den=1e-3
-  
+
 # --enable_perception_obstacles=false
 # --parking_inwards=false
 # --use_dual_variable_warm_start=true