Centralized thread cancellation in processor_t

This ensures that no threads are active when plugins and the rest of the
daemon are unloaded.

callback_job_t was simplified a lot in the process as its main
functionality is now contained in processor_t.  The parent-child
relationships were abandoned as these were only needed to simplify job
cancellation.

src/libhydra/plugins/kernel_pfkey/kernel_pfkey_ipsec.c

@@ -172,11 +172,6 @@ struct private_kernel_pfkey_ipsec_t
 	 */
 	bool install_routes;
 
-	/**
-	 * job receiving PF_KEY events
-	 */
-	callback_job_t *job;
-
 	/**
 	 * mutex to lock access to the PF_KEY socket
 	 */
@@ -2496,10 +2491,6 @@ METHOD(kernel_ipsec_t, bypass_socket, bool,
 METHOD(kernel_ipsec_t, destroy, void,
 	private_kernel_pfkey_ipsec_t *this)
 {
-	if (this->job)
-	{
-		this->job->cancel(this->job);
-	}
 	if (this->socket > 0)
 	{
 		close(this->socket);
@@ -2592,9 +2583,10 @@ kernel_pfkey_ipsec_t *kernel_pfkey_ipsec_create()
 			return NULL;
 		}
 
-		this->job = callback_job_create_with_prio((callback_job_cb_t)receive_events,
-											this, NULL, NULL, JOB_PRIO_CRITICAL);
-		lib->processor->queue_job(lib->processor, (job_t*)this->job);
+		lib->processor->queue_job(lib->processor,
+			(job_t*)callback_job_create_with_prio(
+					(callback_job_cb_t)receive_events, this, NULL,
+					(callback_job_cancel_t)return_false, JOB_PRIO_CRITICAL));
 	}
 
 	return &this->public;