add t_close_session function

Update the token structures and SC_CloseSession to use the new
token-specific function.

Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>
icsf: add t_close_session and t_final functions

These functions are responsible for freeing data specific to ICSF
sessions, destroying session objects and disconnecting from the remote
host.

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