Bluetooth: Mesh: Fix clearing Friend state upon reset

Not clearing the Friend state could risk invalid timers staying
active, etc.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
diff --git a/subsys/bluetooth/host/mesh/main.c b/subsys/bluetooth/host/mesh/main.c
index 69fc1ea..092d340 100644
--- a/subsys/bluetooth/host/mesh/main.c
+++ b/subsys/bluetooth/host/mesh/main.c
@@ -120,6 +120,10 @@
 		bt_mesh_lpn_disable(true);
 	}
 
+	if (IS_ENABLED(CONFIG_BT_MESH_FRIEND)) {
+		bt_mesh_friend_clear_net_idx(BT_MESH_KEY_ANY);
+	}
+
 	if (IS_ENABLED(CONFIG_BT_MESH_GATT_PROXY)) {
 		bt_mesh_proxy_gatt_disable();
 	}