benchmark/latmus: latmon: re-instate warm-up time

Add back a 1s warm-up time, making sure not to include the delta
values collected during this period in the histogram distribution this
time.

Signed-off-by: Philippe Gerum <rpm@xenomai.org>

benchmarks/zephyr/latmon/src/main.c

@@ -244,7 +244,7 @@ static void gpio_ack_handler(struct device *port,
 
 static int monitor(void)
 {
-	u32_t pulse_date, delta, delta_ns, delta_usecs;
+	u32_t pulse_date, delta, delta_ns, delta_usecs, warmup_count = 0;
 	unsigned int key;
 	int cell;
 
@@ -277,6 +277,11 @@ static int monitor(void)
 			continue;
 		}
 
+		if (warmup_count < max_samples_per_bulk) {
+			warmup_count++;
+			continue;
+		}
+
 		delta = ack_date < pulse_date ? ~pulse_date + 1 + ack_date :
 			ack_date - pulse_date;
 		delta_ns = (u32_t)k_cyc_to_ns_floor64(delta);