tcpreplay -i ens3f0 --multiplier=2 a.pcap b.pcap
only sends a.pcap and hang.

After some source dig in,
timeclear(&first_pkt_ts) in send_packets for second file,
causes pkt_ts_delta very large value so sleep forever.

I tested 4.2.6 and 4.3.0-beta1, all reproduced.