lib: nrf_modem_lib: Use debug logs of expected errnos on backend write

We use -ENOSPC and -ENOSPC to signal from the backend that there
is no space in backend or it is not properly connected. This can
occur from time to time and is not always an error. Though, it can
be noisy in log output. This commit replaces the error logs with
debug level and adds a hint that the backend should be properly
connected.

Signed-off-by: Eivind Jølsgard <[email protected]>

Author: eivindj-nordic

lib/nrf_modem_lib/nrf_modem_lib_trace.c

@@ -261,7 +261,10 @@ static int trace_fragment_write(struct nrf_modem_trace_data *frag)
 		}
 
 		if (ret < 0) {
-			if (ret != -ENOSPC) {
+			if ((ret == -ENOSPC) || (ret == -ENOSR)) {
+				LOG_DBG("trace_backend.write returned with %d", ret);
+				LOG_DBG("Please make sure that the backend is properly connected.");
+			} else {
 				LOG_ERR("trace_backend.write failed with err: %d", ret);
 			}