Initialize the association.

async def _init(self):
        """
        Initialize the association.
        """
        chunk = InitChunk()
        chunk.initiate_tag = self._local_verification_tag
        chunk.advertised_rwnd = self._advertised_rwnd
        chunk.outbound_streams = self._outbound_streams_count
        chunk.inbound_streams = self._inbound_streams_max
        chunk.initial_tsn = self._local_tsn
        self._set_extensions(chunk.params)
        await self._send_chunk(chunk)

        # start T1 timer and enter COOKIE-WAIT state
        self._t1_start(chunk)
        self._set_state(self.State.COOKIE_WAIT)