obs-outputs: Increase librtmp send timeout to 15 seconds

Based on what we're seeing after the release of OBS 28, six seconds is
too low and causes disconnects instead of dropped frames.

plugins/obs-outputs/librtmp/rtmp.c

@@ -488,7 +488,7 @@ RTMP_Reset(RTMP *r)
     r->Link.curStreamIdx = 0;
     r->Link.nStreams = 0;
     r->Link.receiveTimeout = 30;
-    r->Link.sendTimeout = 6;
+    r->Link.sendTimeout = 15;
     r->Link.swfAge = 30;
 }