res_pjsip_pubsub: Hold module reference for publications.

Incoming publications need to ensure that the module remains
loaded for the lifetime of them. This is now done by holding
a reference to the module while the publication exists. This
mirrors that of inbound subscriptions.

ASTERISK-27783

Change-Id: Ia98c95a15e11af25728d5fb3e56e12cda0cfc7c0

res/res_pjsip_pubsub.c

@@ -3091,6 +3091,8 @@ static void publication_destroy_fn(void *obj)
 
 	ao2_cleanup(publication->datastores);
 	ao2_cleanup(publication->endpoint);
+
+	ast_module_unref(ast_module_info->self);
 }
 
 static struct ast_sip_publication *sip_create_publication(struct ast_sip_endpoint *endpoint, pjsip_rx_data *rdata,
@@ -3107,6 +3109,8 @@ static struct ast_sip_publication *sip_create_publication(struct ast_sip_endpoin
 		return NULL;
 	}
 
+	ast_module_ref(ast_module_info->self);
+
 	if (!(publication->datastores = ast_datastores_alloc())) {
 		ao2_ref(publication, -1);
 		return NULL;