Fix: sessiond: leak of filter_expression, bytecode, and exclusion

Fix: sessiond: leak of filter_expression, bytecode, and exclusion

The filter_expression, bytecode, and exclusion arguments are leaked
whenever a client omits the transmission of an event-rule as part of an
enable-event command (a protocol error).

Ensure the three arguments are automatically managed using smart
pointers before performing the protocol consistency check.

Change-Id: I4c4f1d5d7b6acdd215ef34e1fc8f2c4bc81a674a
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>