libbinder: RPC more symmetrical max threads

Now, RpcServer and RpcSession both keep track of their max threads using
the same variable, and the server can therefore request the number of
reverse connections possible.

Bug: 185167543
Test: N/A
Change-Id: Ieaff69c8c2da2faf7598aed7e862601a1fcd7a00
diff --git a/libs/binder/RpcServer.cpp b/libs/binder/RpcServer.cpp
index b146bb0..5ffee06 100644
--- a/libs/binder/RpcServer.cpp
+++ b/libs/binder/RpcServer.cpp
@@ -280,6 +280,7 @@
             server->mSessionIdCounter++;
 
             session = RpcSession::make();
+            session->setMaxThreads(server->mMaxThreads);
             session->setForServer(server,
                                   sp<RpcServer::EventListener>::fromExisting(
                                           static_cast<RpcServer::EventListener*>(server.get())),