Pull streamer out into its own module. (#8917)

automerge

core/tests/gossip.rs

@@ -5,7 +5,7 @@ use rayon::iter::*;
 use solana_core::cluster_info::{ClusterInfo, Node};
 use solana_core::gossip_service::GossipService;
 
-use solana_core::packet::Packet;
+use solana_perf::packet::Packet;
 use solana_sdk::signature::{Keypair, Signer};
 use solana_sdk::timing::timestamp;
 use std::net::UdpSocket;