Export RpcServerConnection for use in Trusty

Dependent CL/code: https://android-review.git.corp.google.com/c/trusty/app/authmgr/+/3342621/2/authmgr-be/lib/src/server.rs#28

Test: compile in Trusty
Bug: 369145005
Change-Id: I70cd4bb8f2b2747d61a4c59749c664c39e43b259

Author: Hasini Gunasinghe

libs/binder/rust/rpcbinder/src/lib.rs

@@ -20,6 +20,8 @@ mod server;
 mod session;
 
 pub use server::RpcServer;
+#[cfg(target_os = "trusty")]
+pub use server::RpcServerConnection;
 #[cfg(not(target_os = "trusty"))]
 pub use server::RpcServerRef;
 pub use session::{FileDescriptorTransportMode, RpcSession, RpcSessionRef};