The number of seconds before the SA expires. When 0, the SA
expiration timer is disabled. The default is 24*3600 = 86400
seconds (i.e., 24 hours). The minimum allowed expiration
timer value is 5*60 = 300 seconds (i.e., 5 minutes). The
maximum value is 86400 seconds (i.e., 24 hours).
Rekeying begins 1 minute prior to SA expiration.