ci/respdiff: keep bufsize towards respdiff at 4K

Note: this commits affects just the small respdiffs, not the big ones.

ci/respdiff/kresd.config

@@ -19,4 +19,8 @@ modules = {
 	'stats',    -- Track internal statistics
 }
 
+-- avoid TC flags returned to respdiff
+local _, up_bs = net.bufsize()
+net.bufsize(4096, up_bs)
+
 verbose(true)