Fix: size of concrete class used in memcpy of base class

Fix: size of concrete class used in memcpy of base class

session rotation condition and evaluation objects' base
class is initialized from a template to set the various
method's function pointers to the functions implementing
their interface.

The memcpy() erroneously uses the "derived" class' size through
sizeof(*obj) rather than the size of the base class through
sizeof(obj->parent).

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>