AP_Scheduler: make overtime margin definable

Also warn about overtime on ESP32 which is most likely to hit it.

libraries/AP_Scheduler/PerfInfo.cpp

@@ -17,6 +17,11 @@ extern const AP_HAL::HAL& hal;
 //  we measure the main loop time
 //
 
+// loops over time by this amount or more won't be counted in filtered loop time (and thus loop rate)
+#ifndef AP_SCHEDULER_OVERTIME_MARGIN_US
+#define AP_SCHEDULER_OVERTIME_MARGIN_US 10000UL
+#endif
+
 // reset - reset all records of loop time to zero
 void AP::PerfInfo::reset()
 {
@@ -140,8 +145,16 @@ void AP::PerfInfo::check_loop_time(uint32_t time_in_micros)
     const uint32_t now = AP_HAL::micros();
     const uint32_t loop_time_us = now - last_check_us;
     last_check_us = now;
-    if (loop_time_us < overtime_threshold_micros + 10000UL) {
+    if (loop_time_us < overtime_threshold_micros + AP_SCHEDULER_OVERTIME_MARGIN_US) {
         filtered_loop_time = 0.99f * filtered_loop_time + 0.01f * loop_time_us * 1.0e-6f;
+    } else {
+        // esp32 is most likely to regularly trigger long loops, might be
+        // helpful for bringup of other boards too
+#if CONFIG_HAL_BOARD == HAL_BOARD_ESP32
+#ifdef SCHEDDEBUG
+        DEV_PRINTF("way overtime: %dus\n", loop_time_us);
+#endif
+#endif
     }
 }