[rkp] Add request/response for ECDSA P256 key pair generation

This cl adds the request and response protocol for the ECDSA P256
key pair generation needed for the IRemotelyProvisionedComponent
implementation.

Bug: 299055662
Test: atest rialto_test
Change-Id: Ib3b8519e3833a6617fc6daa878777b9e0499f751
diff --git a/rialto/src/main.rs b/rialto/src/main.rs
index b34b9de..0ecbe9d 100644
--- a/rialto/src/main.rs
+++ b/rialto/src/main.rs
@@ -135,7 +135,7 @@
     debug!("Found socket device: guest cid = {:?}", socket_device.guest_cid());
 
     let mut vsock_stream = VsockStream::new(socket_device, host_addr())?;
-    let response = requests::process_request(vsock_stream.read_request()?);
+    let response = requests::process_request(vsock_stream.read_request()?)?;
     vsock_stream.write_response(&response)?;
     vsock_stream.flush()?;
     vsock_stream.shutdown()?;