[nrf fromtree] net: Added configuring child timeouts on openthread start

Some time ago three Kconfigs dedicated for the child timeouts
configuration were added, but changing them does not apply when
using OpenThread libraries. Added setting these values using
openthread API on openthread start.

Signed-off-by: Kamil Kasperczyk <kamil.kasperczyk@nordicsemi.no>
(cherry picked from commit 2534dc14b9557094cb902e1814bf7bd50a2c39ac)

subsys/net/l2/openthread/openthread.c

@@ -21,6 +21,7 @@ LOG_MODULE_REGISTER(net_l2_openthread, CONFIG_OPENTHREAD_L2_LOG_LEVEL);
 #include <zephyr/sys/__assert.h>
 #include <zephyr/version.h>
 
+#include <openthread/child_supervision.h>
 #include <openthread/cli.h>
 #include <openthread/ip6.h>
 #include <openthread/link.h>
@@ -442,6 +443,13 @@ int openthread_start(struct openthread_context *ot_context)
 		otLinkSetPollPeriod(ot_context->instance, OT_POLL_PERIOD);
 	}
 
+	/* Configure Child Supervision and MLE Child timeouts. */
+	otChildSupervisionSetInterval(ot_context->instance,
+				      CONFIG_OPENTHREAD_CHILD_SUPERVISION_INTERVAL);
+	otChildSupervisionSetCheckTimeout(ot_context->instance,
+					  CONFIG_OPENTHREAD_CHILD_SUPERVISION_CHECK_TIMEOUT);
+	otThreadSetChildTimeout(ot_context->instance, CONFIG_OPENTHREAD_MLE_CHILD_TIMEOUT);
+
 	if (otDatasetIsCommissioned(ot_instance)) {
 		/* OpenThread already has dataset stored - skip the
 		 * configuration.