[rpc_binder] Adjust return when raw socket is not set up

This cl adjusts the return in RpcServer::setupRawSocketServer()
when the socket_fd is not set up. Prior to this cl, errno is
returned. This can be confusing as errno is not always set up in
this case. The current CL fixed this and logged more clear
information.

Test: atest binderRpcTest
Bug: 222479468
Change-Id: Ic9718cbf3cf08befe4044e7f5f021b915b4c4c41
diff --git a/libs/binder/RpcServer.cpp b/libs/binder/RpcServer.cpp
index 399667d..bd72a53 100644
--- a/libs/binder/RpcServer.cpp
+++ b/libs/binder/RpcServer.cpp
@@ -565,12 +565,9 @@
 }
 
 status_t RpcServer::setupRawSocketServer(base::unique_fd socket_fd) {
+    LOG_ALWAYS_FATAL_IF(!socket_fd.ok(), "Socket must be setup to listen.");
     RpcTransportFd transportFd(std::move(socket_fd));
-    if (!transportFd.fd.ok()) {
-        int savedErrno = errno;
-        ALOGE("Could not get initialized Unix socket: %s", strerror(savedErrno));
-        return -savedErrno;
-    }
+
     // Right now, we create all threads at once, making accept4 slow. To avoid hanging the client,
     // the backlog is increased to a large number.
     // TODO(b/189955605): Once we create threads dynamically & lazily, the backlog can be reduced