Rework MGS internals to use SingleSp

The changes include:

* Removal of `RecvHandler` and all its supporting machinery; instead of
  a monster tokio task reponsible for recv'ing on all sockets, pairing
  up request/response IDs, etc., we spawn a `SingleSp` task for each
  switch port that manages all communication on that port's socket.
* Removal of the `timeout` option to most SP calls. `SingleSp` already
  has inherent (configured) timeouts for retries. At the HTTP client
  level, the client can already establish its own timeouts (e.g., in the
  event the network connection between client and server goes down); we
  don't need separate timeouts for SP communications (which the client
  has no reason to know how to set).
* The serial console websocket handling has moved from
  `gateway-sp-comms` to `gateway`.

gateway-cli/src/main.rs

@@ -18,13 +18,16 @@ use slog::o;
 use slog::Drain;
 use slog::Level;
 use slog::Logger;
+use std::borrow::Cow;
 use std::net::IpAddr;
 use std::net::ToSocketAddrs;
 use std::time::Duration;
 use tokio::io::AsyncReadExt;
 use tokio::io::AsyncWriteExt;
 use tokio::net::TcpStream;
 use tokio::select;
+use tokio_tungstenite::tungstenite::protocol::frame::coding::CloseCode;
+use tokio_tungstenite::tungstenite::protocol::CloseFrame;
 use tokio_tungstenite::tungstenite::Message;
 use tokio_tungstenite::MaybeTlsStream;
 use tokio_tungstenite::WebSocketStream;
@@ -281,6 +284,10 @@ async fn main() -> Result<()> {
                 match c {
                     None => {
                         // channel is closed
+                        _ = ws.close(Some(CloseFrame {
+                            code: CloseCode::Normal,
+                            reason: Cow::Borrowed("client closed stdin"),
+                        })).await;
                         break;
                     }
                     Some(c) => {

gateway-sp-comms/Cargo.toml

@@ -6,16 +6,11 @@ license = "MPL-2.0"
 
 [dependencies]
 futures = "0.3.21"
-http = "0.2.7"
-hyper = "0.14.20"
-ringbuffer = "0.8"
 serde = { version = "1.0", features = ["derive"] }
 serde_with = "2.0.0"
 thiserror = "1.0.31"
-tokio-tungstenite = "0.17"
 tokio-stream = "0.1.8"
 usdt = "0.3.1"
-uuid = "1.1.0"
 
 gateway-messages = { path = "../gateway-messages", features = ["std"] }
 omicron-common = { path = "../common" }