uorb: enure message definitions don't exceed buffer lengths & increase test buffer

There were already checks at runtime, but this ensures the format is not
too long at built-time.

src/modules/logger/logger.cpp

@@ -69,6 +69,10 @@
 
 //#define DBGPRINT //write status output every few seconds
 
+static_assert(uORB::orb_untokenized_fields_max_length < sizeof(ulog_message_format_s::format) -
+	      HEATSHRINK_DECODER_INPUT_BUFFER_SIZE(_),
+	      "msg definition too long / buffer too short");
+
 #if defined(DBGPRINT)
 // needed for mallinfo
 #if defined(__PX4_POSIX) && !defined(__PX4_DARWIN)