icsf: use a RW lock for sessions

Change the way the sessions list is protected, replacing the futex with
a RW lock for that.

Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>
icsf: fix wrong variable sid in destroy_objects

Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>