logger: free up ~200B stack size

we now use the already existing buffer for logging messages, which is
allocated on the heap.
In fact, stack usage was too high before this, now it's ok again.

src/modules/logger/logger.cpp

@@ -476,6 +476,10 @@ void Logger::run()
 
 	max_msg_size += sizeof(ulog_message_data_header_s);
 
+	if (sizeof(ulog_message_logging_s) > max_msg_size) {
+		max_msg_size = sizeof(ulog_message_logging_s);
+	}
+
 	if (max_msg_size > _msg_buffer_len) {
 		if (_msg_buffer) {
 			delete[](_msg_buffer);
@@ -596,16 +600,20 @@ void Logger::run()
 			//check for new mavlink log message
 			if (mavlink_log_sub.check_updated()) {
 				mavlink_log_sub.update();
-				ulog_message_logging_s log_msg;
-				log_msg.log_level = mavlink_log_sub.get().severity + '0';
-				log_msg.timestamp = mavlink_log_sub.get().timestamp;
 				const char *message = (const char *)mavlink_log_sub.get().text;
 				int message_len = strlen(message);
 
 				if (message_len > 0) {
-					strncpy(log_msg.message, message, sizeof(log_msg.message));
+					uint16_t write_msg_size = sizeof(ulog_message_logging_s) - sizeof(ulog_message_logging_s::message)
-					log_msg.msg_size = sizeof(log_msg) - sizeof(log_msg.message) - ULOG_MSG_HEADER_LEN + message_len;
+							- ULOG_MSG_HEADER_LEN + message_len;
-					write(&log_msg, log_msg.msg_size + ULOG_MSG_HEADER_LEN);
+					_msg_buffer[0] = (uint8_t)write_msg_size;
+					_msg_buffer[1] = (uint8_t)(write_msg_size >> 8);
+					_msg_buffer[2] = static_cast<uint8_t>(ULogMessageType::LOGGING);
+					_msg_buffer[3] = mavlink_log_sub.get().severity + '0';
+					memcpy(_msg_buffer+4, &mavlink_log_sub.get().timestamp, sizeof(ulog_message_logging_s::timestamp));
+					strncpy((char*)(_msg_buffer+12), message, sizeof(ulog_message_logging_s::message));
+
+					write(_msg_buffer, write_msg_size + ULOG_MSG_HEADER_LEN);
 				}
 			}
 

src/modules/logger/messages.h

@@ -115,7 +115,7 @@ struct ulog_message_logging_s {
 
 	uint8_t log_level; //same levels as in the linux kernel
 	uint64_t timestamp;
-	char message[255];
+	char message[200];
 };
 
 struct ulog_message_parameter_header_s {