Use NGHTTP3 prefix instead of NGTCP2 for errors in h3 callbacks.

[moritzbuhl]

To my understanding the functions are nghttp3 callbacks and should therefore return NGHTTP3_ERR_CALLBACK_FAILURE.
However, this is not critical as the nghttp3 documentation states for all callbacks: (https://nghttp2.org/nghttp3/types.html#c.nghttp3_stop_sending)

The implementation of this callback must return 0 if it succeeds. Returning NGHTTP3_ERR_CALLBACK_FAILURE will return to the caller immediately. Any values other than 0 is treated as NGHTTP3_ERR_CALLBACK_FAILURE.

For nghttp3_strerror, a nghttp3 function sets rc, so I expect a nghttp3 function to transform the error correctly.
The values for NGHTTP3_ERR_... and NGTCP2_ERR_... are not the same, so I expect this to be more relevant.

[bagder]

Nice catch!

[bagder]

Thanks!