acl-plugin: fix the high cpu usage caused by the connection cleaner
acl-plugin: fix the high cpu usage caused by the connection cleaner

The commit 4bc1796b346efd10f3fb19b176ff089179263a24 had incorrect
calculation of the session lists minimal timeout, resulting
in returned value of 0 which resulted in existing sessions
constantly requeued, taking up the CPU. Fix this calculation.

Change-Id: I9a789739f96a1f01522c68f91b0a02db2417837f
Signed-off-by: Andrew Yourtchenko <eb6233fe2fbd585844f4fb8426b53b186ab379b1@gmail.com>

chrisy/vpp,FDio/vpp,FDio/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp,vpp-dev/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,vpp-dev/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,vpp-dev/vpp,chrisy/vpp,chrisy/vpp,vpp-dev/vpp,vpp-dev/vpp,FDio/vpp,vpp-dev/vpp