Add Host.ConnectLEWithUpdates rpc

Add Host.ConnectLEWithUpdates rpc that will be used to receive
connection parameter updates in Pandora tests. A stream is used
so that no updates are missed, especially right after connecting.
The stream can also be used in the future for connection updates
like encryption being enabled.

pandora/host.proto

@@ -59,6 +59,10 @@ service Host {
   // Unlike BR/EDR `Connect`, this must not trigger or wait any
   // pairing/encryption and return as soon as the connection is complete.
   rpc ConnectLE(ConnectLERequest) returns (ConnectLEResponse);
+  // Like `ConnectLE`, but streams updates about the connection after the
+  // initial ConnectLEResponse. Currently the only update supported is
+  // connection parameter updates.
+  rpc ConnectLEWithUpdates(ConnectLERequest) returns (stream ConnectLEWithUpdatesResponse);
   // Disconnect an ACL connection.
   // The related Connection must not be reused afterwards.
   rpc Disconnect(DisconnectRequest) returns (google.protobuf.Empty);
@@ -257,6 +261,34 @@ message ConnectLEResponse {
   }
 }
 
+// Response of the `ConnectLEWithUpdates` method.
+message ConnectLEWithUpdatesResponse {
+  oneof update {
+    // The first message sent on the stream. Contains the Connection on success
+    // or an error on failure.
+    ConnectLEResponse connect_response = 1;
+    // Sent when the connection parameters are updated.
+    ConnectionParameters connection_parameter_update = 2;
+  }
+}
+
+message ConnectionParameters {
+  // Connection interval used on this connection.
+  // Range: 0x0006 to 0x0C80
+  // Time = N × 1.25 ms
+  // Time Range: 7.5 ms to 4000 ms.
+  uint16 connection_interval = 1;
+  // Peripheral latency for the connection in number of subrated connection
+  // events.
+  // Range: 0x0000 to 0x01F3
+  uint16 peripheral_latency = 2;
+  // Supervision timeout for this connection.
+  // Range: 0x000A to 0x0C80
+  // Time = N × 10 ms
+  // Time Range: 100 ms to 32000 ms
+  uint16 supervision_timeout = 3;
+}
+
 // Request of the `Disconnect` method.
 message DisconnectRequest {
   // Connection that should be disconnected.