obs-ffmpeg: Change default nvenc preset to P5

P6 seems to invoke lookahead, which causes lag for some older GPUs and
interferes with game performance. So let's just use P5 by default for
now. Shouldn't really affect recording anyway.

plugins/obs-ffmpeg/obs-ffmpeg-nvenc.c

@@ -428,7 +428,7 @@ static void nvenc_defaults_base(enum codec_type codec, obs_data_t *settings)
 	obs_data_set_default_int(settings, "keyint_sec", 0);
 	obs_data_set_default_int(settings, "cqp", 20);
 	obs_data_set_default_string(settings, "rate_control", "CBR");
-	obs_data_set_default_string(settings, "preset2", "p6");
+	obs_data_set_default_string(settings, "preset2", "p5");
 	obs_data_set_default_string(settings, "multipass", "qres");
 	obs_data_set_default_string(settings, "tune", "hq");
 	obs_data_set_default_string(settings, "profile",