binder: RpcTransport: change to size_t.

- Change return type to Result<size_t> because negative numbers
  (-1) are converted to an Error().
- Change size argument from int to size_t because size_t is unsigned
  and is the best type to represent a "size".

Test: pass
Bug: 190868302
Fixes: 195592175
Change-Id: Ide26d2d5cc11a9b776fc3dc0a2281300f611b327
diff --git a/libs/binder/RpcTransportRaw.cpp b/libs/binder/RpcTransportRaw.cpp
index 953d233..2fc1945 100644
--- a/libs/binder/RpcTransportRaw.cpp
+++ b/libs/binder/RpcTransportRaw.cpp
@@ -32,21 +32,21 @@
 class RpcTransportRaw : public RpcTransport {
 public:
     explicit RpcTransportRaw(android::base::unique_fd socket) : mSocket(std::move(socket)) {}
-    Result<ssize_t> send(const void *buf, int size) override {
+    Result<size_t> send(const void *buf, size_t size) override {
         ssize_t ret = TEMP_FAILURE_RETRY(::send(mSocket.get(), buf, size, MSG_NOSIGNAL));
         if (ret < 0) {
             return ErrnoError() << "send()";
         }
         return ret;
     }
-    Result<ssize_t> recv(void *buf, int size) override {
+    Result<size_t> recv(void *buf, size_t size) override {
         ssize_t ret = TEMP_FAILURE_RETRY(::recv(mSocket.get(), buf, size, MSG_NOSIGNAL));
         if (ret < 0) {
             return ErrnoError() << "recv()";
         }
         return ret;
     }
-    Result<ssize_t> peek(void *buf, int size) override {
+    Result<size_t> peek(void *buf, size_t size) override {
         ssize_t ret = TEMP_FAILURE_RETRY(::recv(mSocket.get(), buf, size, MSG_PEEK | MSG_DONTWAIT));
         if (ret < 0) {
             return ErrnoError() << "recv(MSG_PEEK)";