Add a DirectedGossip struct (#6803)

* Add a DirectedGossip struct

* Move protocol from prototype::new to biuld

* More traits impls

* Explain ordering

* Apply suggestions from code review

Co-authored-by: Toralf Wittner <tw@dtex.org>

* Address concerns

* Add basic test

* Concerns

* More concerns

* Remove QueueSenderPrototype

* Rename

* Apply suggestions from code review

Co-authored-by: Max Inden <mail@max-inden.de>

Co-authored-by: Toralf Wittner <tw@dtex.org>
Co-authored-by: parity-processbot <>
Co-authored-by: Max Inden <mail@max-inden.de>

substrate/client/network/Cargo.toml

@@ -16,6 +16,7 @@ targets = ["x86_64-unknown-linux-gnu"]
 prost-build = "0.6.1"
 
 [dependencies]
+async-std = { version = "1.6.2", features = ["unstable"] }
 bitflags = "1.2.0"
 bs58 = "0.3.1"
 bytes = "0.5.0"
@@ -66,7 +67,6 @@ default-features = false
 features = ["identify", "kad", "mdns", "mplex", "noise", "ping", "tcp-async-std", "websocket", "yamux"]
 
 [dev-dependencies]
-async-std = "1.6.2"
 assert_matches = "1.3"
 env_logger = "0.7.0"
 libp2p = { version = "0.23.0", default-features = false, features = ["secio"] }