dcou test only code in streamer (#6936)

* dcou test only code in streamer
* patch cargo.toml in udp-client

streamer/src/nonblocking/mod.rs

@@ -1,5 +1,6 @@
 pub mod connection_rate_limiter;
 pub mod quic;
+#[cfg(feature = "dev-context-only-utils")]
 pub mod recvmmsg;
 pub mod sendmmsg;
 mod stream_throttle;

udp-client/Cargo.toml

@@ -22,3 +22,4 @@ tokio = { workspace = true, features = ["full"] }
 [dev-dependencies]
 solana-net-utils = { workspace = true, features = ["dev-context-only-utils"] }
 solana-packet = { workspace = true }
+solana-streamer = { workspace = true, features = ["dev-context-only-utils"] }