Add nghttp2_session_check_server_session() API

This is very simple API, and it returns nonzero if session is
initialized as server.

lib/includes/nghttp2/nghttp2.h

@@ -3616,6 +3616,14 @@ nghttp2_session_get_last_proc_stream_id(nghttp2_session *session);
 NGHTTP2_EXTERN int
 nghttp2_session_check_request_allowed(nghttp2_session *session);
 
+/**
+ * @function
+ *
+ * Returns nonzero if |session| is initialized as server side session.
+ */
+NGHTTP2_EXTERN int
+nghttp2_session_check_server_session(nghttp2_session *session);
+
 /**
  * @function
  *

lib/nghttp2_session.c

@@ -6767,3 +6767,7 @@ nghttp2_stream *nghttp2_session_find_stream(nghttp2_session *session,
 nghttp2_stream *nghttp2_session_get_root_stream(nghttp2_session *session) {
   return &session->root;
 }
+
+int nghttp2_session_check_server_session(nghttp2_session *session) {
+  return session->server;
+}