binder: Eliminate a data copy in RPC transport operations

Switch RpcTransportRaw to use sendmsg() and recvmsg() over
iovecs to send data from multiple buffers to avoid having
to copy all data into a single large buffer.

Bug: 202878542
Test: atest binderRpcTest
Change-Id: I8ba7fa815040555503160ae41888a0b0efe9e5d2
diff --git a/libs/binder/RpcState.h b/libs/binder/RpcState.h
index dba0a43..5cad394 100644
--- a/libs/binder/RpcState.h
+++ b/libs/binder/RpcState.h
@@ -24,6 +24,8 @@
 #include <optional>
 #include <queue>
 
+#include <sys/uio.h>
+
 namespace android {
 
 struct RpcWireHeader;
@@ -177,12 +179,12 @@
     };
 
     [[nodiscard]] status_t rpcSend(const sp<RpcSession::RpcConnection>& connection,
-                                   const sp<RpcSession>& session, const char* what,
-                                   const void* data, size_t size,
+                                   const sp<RpcSession>& session, const char* what, iovec* iovs,
+                                   size_t niovs,
                                    const std::function<status_t()>& altPoll = nullptr);
     [[nodiscard]] status_t rpcRec(const sp<RpcSession::RpcConnection>& connection,
-                                  const sp<RpcSession>& session, const char* what, void* data,
-                                  size_t size);
+                                  const sp<RpcSession>& session, const char* what, iovec* iovs,
+                                  size_t niovs);
 
     [[nodiscard]] status_t waitForReply(const sp<RpcSession::RpcConnection>& connection,
                                         const sp<RpcSession>& session, Parcel* reply);