The main difference is that ping now reports icmp_seq instead of
icmp_req, so we match for icmp_.eq, which works with both releases.
tcpdump now also reports port 4500 as ipsec-nat-t.
With -W we reduce timeouts when we don't expect a response. With -i the
interval between pings is reduced (mostly in case of auto=route where
the first ping yields no reply).
Tobias Brunner