batman-adv: reuse tt_len() to calculate tt buffer length

Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Acked-by: Antonio Quartulli <ordex@autistici.org>

net/batman-adv/aggregation.h

@@ -28,8 +28,7 @@
 static inline int aggregated_packet(int buff_pos, int packet_len,
 				    int tt_num_changes)
 {
-	int next_buff_pos = buff_pos + BAT_PACKET_LEN + (tt_num_changes *
-						sizeof(struct tt_change));
+	int next_buff_pos = buff_pos + BAT_PACKET_LEN + tt_len(tt_num_changes);
 
 	return (next_buff_pos <= packet_len) &&
 		(next_buff_pos <= MAX_AGGREGATION_BYTES);