Use android::base::function_ref isntead of std::function

This removes an allocation from the binder RPC calls.

Test: atest binderAllocationLimits
Bug: 230625474
Change-Id: I70ebb4e320323149c3c66809f1077cbf332c07ef
diff --git a/libs/binder/RpcState.h b/libs/binder/RpcState.h
index f4a0894..9cbe187 100644
--- a/libs/binder/RpcState.h
+++ b/libs/binder/RpcState.h
@@ -178,9 +178,10 @@
         size_t mSize;
     };
 
-    [[nodiscard]] status_t rpcSend(const sp<RpcSession::RpcConnection>& connection,
-                                   const sp<RpcSession>& session, const char* what, iovec* iovs,
-                                   int niovs, const std::function<status_t()>& altPoll = nullptr);
+    [[nodiscard]] status_t rpcSend(
+            const sp<RpcSession::RpcConnection>& connection, const sp<RpcSession>& session,
+            const char* what, iovec* iovs, int niovs,
+            const std::optional<android::base::function_ref<status_t()>>& altPoll);
     [[nodiscard]] status_t rpcRec(const sp<RpcSession::RpcConnection>& connection,
                                   const sp<RpcSession>& session, const char* what, iovec* iovs,
                                   int niovs);