RTC: Disable merge_nalus by default

trunk/conf/full.conf

@@ -444,8 +444,8 @@ rtc_server {
     reuseport       1;
     # Whether merge multiple NALUs into one.
     # @see https://github.com/ossrs/srs/issues/307#issuecomment-612806318
-    # default: on
-    merge_nalus     on;
+    # default: off
+    merge_nalus     off;
     # Whether enable the perf stat at http://localhost:1985/api/v1/perf
     # default: on
     perf_stat       on;