Add REBOOTING state support for dhcp client

According to DHCP protocol below:
	rfc2131 4.3.2 DHCPREQUEST generated during INIT-REBOOT state
	rfc2131 4.4.2 Initialization with known network address

For a favorite service which is connected before, when it is connected
again and request IP address through DHCP, it doesn't need to broadcast
DHCPDISCOVER message every time to get the IP address. It can request to
reuse the previously allocated IP address, and broadcast a DHCPREQUEST
message directly and omit the steps such as dhcp DISCOVER/OFFER/SELECT.

gdhcp/client.c

@@ -62,6 +62,7 @@ typedef enum _listen_mode {
 
 typedef enum _dhcp_client_state {
 	INIT_SELECTING,
+	REBOOTING,
 	REQUESTING,
 	BOUND,
 	RENEWING,
@@ -438,6 +439,30 @@ static int send_discover(GDHCPClient *dhcp_client, uint32_t requested)
 					MAC_BCAST_ADDR, dhcp_client->ifindex);
 }
 
+static int send_rebooting(GDHCPClient *dhcp_client)
+{
+	struct dhcp_packet packet;
+	debug(dhcp_client, "sending DHCP rebooting request");
+
+	init_packet(dhcp_client, &packet, DHCPREQUEST);
+
+	packet.xid = dhcp_client->xid;
+	packet.secs = dhcp_attempt_secs(dhcp_client);
+
+	dhcp_add_option_uint32(&packet, DHCP_REQUESTED_IP,
+					dhcp_client->requested_ip);
+
+	dhcp_add_option_uint16(&packet, DHCP_MAX_SIZE, 576);
+
+	add_request_options(dhcp_client, &packet);
+
+	add_send_options(dhcp_client, &packet);
+
+	return dhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT,
+					INADDR_BROADCAST, SERVER_PORT,
+					MAC_BCAST_ADDR, dhcp_client->ifindex);
+}
+
 static int send_select(GDHCPClient *dhcp_client)
 {
 	struct dhcp_packet packet;
@@ -1756,10 +1781,14 @@ static gboolean restart_dhcp_timeout(gpointer user_data)
 
 	debug(dhcp_client, "restart DHCP timeout");
 
-	dhcp_client->ack_retry_times++;
-
-	restart_dhcp(dhcp_client, dhcp_client->ack_retry_times);
-
+	if (dhcp_client->state == REBOOTING) {
+		g_free(dhcp_client->last_address);
+		dhcp_client->last_address = NULL;
+		restart_dhcp(dhcp_client, 0);
+	} else {
+		dhcp_client->ack_retry_times++;
+		restart_dhcp(dhcp_client, dhcp_client->ack_retry_times);
+	}
 	return FALSE;
 }
 
@@ -2330,6 +2359,7 @@ static gboolean listener_event(GIOChannel *channel, GIOCondition condition,
 		start_request(dhcp_client);
 
 		return TRUE;
+	case REBOOTING:
 	case REQUESTING:
 	case RENEWING:
 	case REBINDING:
@@ -2565,6 +2595,22 @@ static gboolean discover_timeout(gpointer user_data)
 	return FALSE;
 }
 
+static gboolean reboot_timeout(gpointer user_data)
+{
+	GDHCPClient *dhcp_client = user_data;
+	dhcp_client->retry_times = 0;
+	dhcp_client->requested_ip = 0;
+	dhcp_client->state = INIT_SELECTING;
+	/*
+	 * We do not send the REQUESTED IP option because the server didn't
+	 * respond when we send DHCPREQUEST with the REQUESTED IP option in
+	 * init-reboot state
+	 */
+	g_dhcp_client_start(dhcp_client, NULL);
+
+	return FALSE;
+}
+
 static gboolean ipv4ll_defend_timeout(gpointer dhcp_data)
 {
 	GDHCPClient *dhcp_client = dhcp_data;
@@ -2753,6 +2799,21 @@ int g_dhcp_client_start(GDHCPClient *dhcp_client, const char *last_address)
 			dhcp_client->last_address = g_strdup(last_address);
 		}
 	}
+
+	if ((addr != 0) && (dhcp_client->type != G_DHCP_IPV4LL)) {
+		debug(dhcp_client, "DHCP client start with state init_reboot");
+		dhcp_client->requested_ip = addr;
+		dhcp_client->state = REBOOTING;
+		send_rebooting(dhcp_client);
+
+		dhcp_client->timeout = g_timeout_add_seconds_full(
+								G_PRIORITY_HIGH,
+								REQUEST_TIMEOUT,
+								reboot_timeout,
+								dhcp_client,
+								NULL);
+		return 0;
+	}
 	send_discover(dhcp_client, addr);
 
 	dhcp_client->timeout = g_timeout_add_seconds_full(G_PRIORITY_HIGH,
@@ -2919,6 +2980,7 @@ char *g_dhcp_client_get_netmask(GDHCPClient *dhcp_client)
 		if (option)
 			return g_strdup(option->data);
 	case INIT_SELECTING:
+	case REBOOTING:
 	case REQUESTING:
 	case RELEASED:
 	case IPV4LL_PROBE: