libbinder: better RpcSession shutdown detail logs

If shutdown was called before, it looked like it failed, when really it
had already completed.

Bug: N/A
Test: N/A
Change-Id: I86183b95b0896fd533bbaa291d09cf44422fec1e
diff --git a/libs/binder/RpcServer.cpp b/libs/binder/RpcServer.cpp
index 2a87ae4..9943e47 100644
--- a/libs/binder/RpcServer.cpp
+++ b/libs/binder/RpcServer.cpp
@@ -182,7 +182,7 @@
 bool RpcServer::shutdown() {
     std::unique_lock<std::mutex> _l(mLock);
     if (mShutdownTrigger == nullptr) {
-        LOG_RPC_DETAIL("Cannot shutdown. No shutdown trigger installed.");
+        LOG_RPC_DETAIL("Cannot shutdown. No shutdown trigger installed (already shutdown?)");
         return false;
     }
 
@@ -212,6 +212,8 @@
         mJoinThread.reset();
     }
 
+    LOG_RPC_DETAIL("Finished waiting on shutdown.");
+
     mShutdownTrigger = nullptr;
     return true;
 }