libbinder: support TF_CLEAR_BUF

This flag instructs the kernel to clear transactions from send/reply
buffers for certain transactions which may contain sensitive data, as a
security precaution.

Bug: 171501998
Test: binderLibTest (only checks there is no error)
Change-Id: I69d732e5cc2b15472dc52d47c66716bc1b3be6ae
diff --git a/libs/binder/rust/src/binder.rs b/libs/binder/rust/src/binder.rs
index 6d0a369..037ee95 100644
--- a/libs/binder/rust/src/binder.rs
+++ b/libs/binder/rust/src/binder.rs
@@ -33,8 +33,7 @@
 
 /// Additional operation flags.
 ///
-/// Can be either 0 for a normal RPC, or [`IBinder::FLAG_ONEWAY`] for a
-/// one-way RPC.
+/// `IBinder::FLAG_*` values.
 pub type TransactionFlags = u32;
 
 /// Super-trait for Binder interfaces.
@@ -91,6 +90,8 @@
 
     /// Corresponds to TF_ONE_WAY -- an asynchronous call.
     const FLAG_ONEWAY: TransactionFlags = sys::FLAG_ONEWAY;
+    /// Corresponds to TF_CLEAR_BUF -- clear transaction buffers after call is made.
+    const FLAG_CLEAR_BUF: TransactionFlags = sys::FLAG_CLEAR_BUF;
 
     /// Is this object still alive?
     fn is_binder_alive(&self) -> bool;