[network/notifications] A remote peer is not backed off when it rejects a substream

[dmitry-markin]

When the remote closes the entire connection, it's backed off, while if it closes a substream only, it's not.
When the remote closes the entire connection, the back-off is introduced here:

polkadot-sdk/substrate/client/network/src/protocol/notifications/behaviour.rs

Lines 1342 to 1358 in 76724ce

	let ban_dur = Uniform::new(5, 10).sample(&mut rand::thread_rng());
	let delay_id = self.next_delay_id;
	self.next_delay_id.0 += 1;
	let delay = futures_timer::Delay::new(Duration::from_secs(ban_dur));
	self.delays.push(
	async move {
	delay.await;
	(delay_id, peer_id, set_id)
	}
	.boxed(),
	);
	*entry.get_mut() = PeerState::Backoff {
	timer: delay_id,
	timer_deadline: Instant::now() + Duration::from_secs(ban_dur),
	};

At the same time, if the remote just closes a substream, no back-off is applied here:

polkadot-sdk/substrate/client/network/src/protocol/notifications/behaviour.rs

Lines 1744 to 1745 in 76724ce

	*entry.into_mut() =
	PeerState::Disabled { connections, backoff_until: None };

Originally discussed in #1563 (comment).

Relates to paritytech/substrate#13778.