batman-adv: add build check macros for packet member offset

Since we removed the __packed from most of the packets, we should
make sure that the offset generated by the compiler are correct for
sent/received data.
Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>

net/batman-adv/main.c

@@ -393,6 +393,14 @@ static void batadv_recv_handler_init(void)
 	for (i = 0; i < ARRAY_SIZE(batadv_rx_handler); i++)
 		batadv_rx_handler[i] = batadv_recv_unhandled_packet;
 
+	/* compile time checks for struct member offsets */
+	BUILD_BUG_ON(offsetof(struct batadv_unicast_4addr_packet, src) != 10);
+	BUILD_BUG_ON(offsetof(struct batadv_unicast_packet, dest) != 4);
+	BUILD_BUG_ON(offsetof(struct batadv_unicast_frag_packet, dest) != 4);
+	BUILD_BUG_ON(offsetof(struct batadv_unicast_tvlv_packet, dst) != 4);
+	BUILD_BUG_ON(offsetof(struct batadv_icmp_packet, dst) != 4);
+	BUILD_BUG_ON(offsetof(struct batadv_icmp_packet_rr, dst) != 4);
+
 	/* batman icmp packet */
 	batadv_rx_handler[BATADV_ICMP] = batadv_recv_icmp_packet;
 	/* unicast with 4 addresses packet */