base: close PD session last when destructing child

This patch moves the destruction of the child's PD session after the
closing of all other sessions because the PD session's role as resource
container might still be needed for orderly reverting the session quotas
when closing the other remaining sessions.

Issue #4917

repos/base/src/lib/base/child.cc

@@ -889,7 +889,6 @@ void Child::close_all_sessions()
 	_binary.close();
 	if (_linker.constructed())
 		_linker->close();
-	_pd.close();
 
 	/*
 	 * Remove statically created env sessions from the child's ID space.
@@ -915,6 +914,8 @@ void Child::close_all_sessions()
 
 	while (_id_space.apply_any<Session_state>(close_fn));
 
+	_pd.close();
+
 	if (!KERNEL_SUPPORTS_EAGER_CHILD_DESTRUCTION)
 		_cpu._connection.destruct();
 }