Submits GOAWAY frame with the last stream ID *last_stream_id* and
the error code *error_code*.

The pre-defined error code is one of :enum:`nghttp2_error_code`.

The *flags* is currently ignored and should be
:enum:`nghttp2_flag.NGHTTP2_FLAG_NONE`.

The *last_stream_id* is peer's stream ID or 0.  So if *session* is
initialized as client, *last_stream_id* must be even or 0.  If
*session* is initialized as server, *last_stream_id* must be odd or
0.

The HTTP/2 specification says last_stream_id must not be increased
from the value previously sent.  So the actual value sent as
last_stream_id is the minimum value between the given
*last_stream_id* and the last_stream_id previously sent to the
peer.

If the *opaque_data* is not ``NULL`` and *opaque_data_len* is not
zero, those data will be sent as additional debug data.  The
library makes a copy of the memory region pointed by *opaque_data*
with the length *opaque_data_len*, so the caller does not need to
keep this memory after the return of this function.  If the
*opaque_data_len* is 0, the *opaque_data* could be ``NULL``.

After successful transmission of GOAWAY, following things happen.
All incoming streams having strictly more than *last_stream_id* are
closed.  All incoming HEADERS which starts new stream are simply
ignored.  After all active streams are handled, both
`nghttp2_session_want_read()` and `nghttp2_session_want_write()`
return 0 and the application can close session.

This function returns 0 if it succeeds, or one of the following
negative error codes:

:enum:`nghttp2_error.NGHTTP2_ERR_NOMEM`
    Out of memory.
:enum:`nghttp2_error.NGHTTP2_ERR_INVALID_ARGUMENT`
    The *opaque_data_len* is too large; the *last_stream_id* is
    invalid.