logging: init backend id regardless of autostart

The `id` is basically a compile-time constant. Setting it every
time the backend is enabled is unnecessary. Instead, set it on
`z_log_init()` regardless of whether or not it requires to be
`autostart`ed.

Fixes an issue where the `filter_get`/`filter_set`
accessed the wrong index and displayed the wrong log level when
user accesses the status of an uninitialized backend via:
`log backend <uninitialized_backend> status`.

Also fixes an issue when user tries to list the backends via:
`log list_backends`, where all uninitialized backends will have
ID = 0.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>
Signed-off-by: Yong Cong Sin <yongcong.sin@gmail.com>
(cherry picked from commit 8dd9d924fe)

subsys/logging/log_core.c

@@ -328,8 +328,14 @@ static uint32_t z_log_init(bool blocking, bool can_sleep)
 
 	int backend_index = 0;
 
-	/* Activate autostart backends */
 	STRUCT_SECTION_FOREACH(log_backend, backend) {
+		uint32_t id;
+		/* As first slot in filtering mask is reserved, backend ID has offset.*/
+		id = LOG_FILTER_FIRST_BACKEND_SLOT_IDX;
+		id += backend - log_backend_get(0);
+		log_backend_id_set(backend, id);
+
+		/* Activate autostart backends */
 		if (backend->autostart) {
 			log_backend_init(backend);
 

subsys/logging/log_mgmt.c

@@ -553,12 +553,6 @@ void log_backend_enable(struct log_backend const *const backend,
 			void *ctx,
 			uint32_t level)
 {
-	/* As first slot in filtering mask is reserved, backend ID has offset.*/
-	uint32_t id = LOG_FILTER_FIRST_BACKEND_SLOT_IDX;
-
-	id += backend - log_backend_get(0);
-
-	log_backend_id_set(backend, id);
 	backend->cb->level = level;
 	backend_filter_set(backend, level);
 	log_backend_activate(backend, ctx);