Uses the `NgHttp2Session::perspective_` member, which is otherwise unused and causes Envoy build errors.

PiperOrigin-RevId: 400215775
diff --git a/http2/adapter/nghttp2_session.cc b/http2/adapter/nghttp2_session.cc
index 2e1fdfa..13867bd 100644
--- a/http2/adapter/nghttp2_session.cc
+++ b/http2/adapter/nghttp2_session.cc
@@ -10,7 +10,7 @@
                                const nghttp2_option* options, void* userdata)
     : session_(MakeSessionPtr(nullptr)), perspective_(perspective) {
   nghttp2_session* session;
-  switch (perspective) {
+  switch (perspective_) {
     case Perspective::kClient:
       nghttp2_session_client_new2(&session, callbacks.get(), userdata, options);
       break;