mesh: Fix Node Identity advertising with PB-ADV

The Node Identity advertising should only be automatically enabled
when provisioning happened over PB-GATT, but not when it happened over
PB-ADV. Move the enabling of Node Identity to the provisioning code,
where we know the bearer that was used (this information does not get
passed to the bt_mesh_provision function).

nimble/host/mesh/src/net.c

@@ -476,8 +476,7 @@ int bt_mesh_net_create(u16_t idx, u8_t flags, const u8_t key[16],
 	sub->net_idx = idx;
 
 	if ((MYNEWT_VAL(BLE_MESH_GATT_PROXY))) {
-		sub->node_id = BT_MESH_NODE_IDENTITY_RUNNING;
-		sub->node_id_start = k_uptime_get_32();
+		sub->node_id = BT_MESH_NODE_IDENTITY_STOPPED;
 	} else {
 		sub->node_id = BT_MESH_NODE_IDENTITY_NOT_SUPPORTED;
 	}

nimble/host/mesh/src/prov.c

@@ -1073,6 +1073,13 @@ static void prov_data(const u8_t *data)
 
 	bt_mesh_provision(pdu, net_idx, flags, iv_index, 0, addr, dev_key);
 
+#if MYNEWT_VAL(BLE_MESH_PB_GATT) && MYNEWT_VAL(BLE_MESH_GATT_PROXY)
+	/* After PB-GATT provisioning we should start advertising
+	 * using Node Identity.
+	 */
+	bt_mesh_proxy_identity_enable();
+#endif
+
 done:
 	os_mbuf_free_chain(msg);
 }