tests: net: dhcpv6: Reapply LL address on iface up

The test suite assigns LL address to the interface manually, hence need
to reapply it whenever interface goes up.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>

tests/net/dhcpv6/src/main.c

@@ -8,6 +8,7 @@
 #include <zephyr/net/dummy.h>
 #include <zephyr/net/ethernet.h>
 #include <zephyr/net/net_if.h>
+#include <zephyr/net/net_mgmt.h>
 
 #include "../../../subsys/net/lib/dhcpv6/dhcpv6.c"
 
@@ -18,6 +19,7 @@ static struct in6_addr test_prefix = { { { 0x20, 0x01, 0x0d, 0xb8, 0, 0, 0, 0,
 static uint8_t test_prefix_len = 64;
 static uint8_t test_preference;
 static struct net_dhcpv6_duid_storage test_serverid;
+static struct net_mgmt_event_callback net_mgmt_cb;
 
 typedef void (*test_dhcpv6_pkt_fn_t)(struct net_if *iface,
 				     struct net_pkt *pkt);
@@ -176,6 +178,19 @@ static struct net_pkt *test_dhcpv6_create_message(
 	return NULL;
 }
 
+static void evt_handler(struct net_mgmt_event_callback *cb, uint32_t mgmt_event,
+			struct net_if *iface)
+{
+	ARG_UNUSED(cb);
+
+	if (mgmt_event == NET_EVENT_IF_UP) {
+		struct in6_addr lladdr;
+
+		net_ipv6_addr_create_iid(&lladdr, net_if_get_link_addr(test_ctx.iface));
+		(void)net_if_ipv6_addr_add(test_ctx.iface, &lladdr, NET_ADDR_AUTOCONF, 0);
+	}
+}
+
 static void *dhcpv6_tests_setup(void)
 {
 	struct in6_addr lladdr;
@@ -190,6 +205,9 @@ static void *dhcpv6_tests_setup(void)
 
 	generate_fake_server_duid();
 
+	net_mgmt_init_event_callback(&net_mgmt_cb, evt_handler, NET_EVENT_IF_UP);
+	net_mgmt_add_event_callback(&net_mgmt_cb);
+
 	return NULL;
 }