logging: log_core: correct timeout of -1 ms to K_FOREVER

Many releases ago, specifying to block indefinitely in the log
processing thread would do just that.

However, a subtle bug was introduced  such that specifying -1
for `CONFIG_LOG_BLOCK_IN_THREAD_TIMEOUT_MS` would have the
exact opposite effect than what was intended.

As per Kconfig, a value of -1 should translate to a timeout of
`K_FOREVER`. However, conversion via `K_MSEC(-1)` results in
a `k_timeout_t` that is equal to `K_NO_WAIT` rather than the
intent which is `K_FOREVER`.

Add a dedicated check to to ensure that a value of -1 is
correctly interpreted as `K_FOREVER` in `log_core.c`.

For reference, the blocking feature was described in #15196,
added in #16194, and it would appear that the regression
happened in c5f2cde.

(cherry picked from commit 137097f)

Original-Signed-off-by: Christopher Friedt <cfriedt@meta.com>
GitOrigin-RevId: 137097f
Change-Id: I2ee43e9626e063a7de0a536e05452db337411b73
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/4942110
Reviewed-by: Keith Short <keithshort@chromium.org>
Tested-by: Keith Short <keithshort@chromium.org>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Commit-Queue: Keith Short <keithshort@chromium.org>

subsys/logging/log_core.c

@@ -597,8 +597,11 @@ static struct log_msg *msg_alloc(struct mpsc_pbuf_buffer *buffer, uint32_t wlen)
 		return NULL;
 	}
 
-	return (struct log_msg *)mpsc_pbuf_alloc(buffer, wlen,
-				K_MSEC(CONFIG_LOG_BLOCK_IN_THREAD_TIMEOUT_MS));
+	return (struct log_msg *)mpsc_pbuf_alloc(
+		buffer, wlen,
+		(CONFIG_LOG_BLOCK_IN_THREAD_TIMEOUT_MS == -1)
+			? K_FOREVER
+			: K_MSEC(CONFIG_LOG_BLOCK_IN_THREAD_TIMEOUT_MS));
 }
 
 struct log_msg *z_log_msg_alloc(uint32_t wlen)