Add log function to demo server

Signed-off-by: Xiaofeng Lin <jerrylin.lxf@gmail.com>
Delete library debug print

Signed-off-by: Xiaofeng Lin <jerrylin.lxf@gmail.com>
Adjust RLIMIT_CORE and RLIMIT_NOFILE setting of demo server

Signed-off-by: Xiaofeng Lin <jerrylin.lxf@gmail.com>
Fix bug in the session closing stage

Signed-off-by: Xiaofeng Lin <jerrylin.lxf@gmail.com>
Set linger to back end socket to reduce TIME-WAIT sockets

Signed-off-by: Xiaofeng Lin <jerrylin.lxf@gmail.com>