This test sets a soft byte lifetime, and sends a number of packets.

The console output, via "ipsec pf_key" shows a single expire message from the
kernel:

pfkey v2 msg. type=8 seq=1 len=20 pid=987 errno=0 satype=3
pfkey_lib_debug:pfkey_msg_parse: parsing message ver=2, type=8(expire), errno=0, satype=3(ESP), len=20, res=0, seq=1, pid=0.
pfkey_lib_debug:pfkey_msg_parse: remain=18, ext_type=1(security-association), ext_len=2.
...