s4:tevent: Increase trace debug level to 50.

The sheer volume of messages generated by tevent when the trace level is set to
10 makes it difficult to debug issues in a level 10 log.  Increasing this to
50 allows tevent tracing to be enabled if needed, but otherwise keeps the extra
chatter out of a level 10 log.

source4/lib/events/tevent_s4.c

@@ -42,7 +42,7 @@ static void ev_wrap_debug(void *context, enum tevent_debug_level level,
 		samba_level = 2;
 		break;
 	case TEVENT_DEBUG_TRACE:
-		samba_level = 10;
+		samba_level = 50;
 		break;
 
 	};