Only start measuring once the first packet is received

packet-exchange/src/server.c

@@ -123,12 +123,12 @@ static void *packet_receiving_thread(void *p) {
 
       int current_packet_id;
 
+      recv_udp_packet();
+
       clock_gettime(CLOCK_MONOTONIC, &current);
 
-      recv_udp_packet();
       current_packet_id = atoi(ingress_stats.data);
 
-      // If this is not the first received packet
       if (ingress_stats.packets_received) {
         int interval_us = calcdiff_ns(current, previous) / 1000;