When creating objects in the upper layer we need to pass down the upper
idmapping into the respective vfs helpers in order to support idmapped
base layers. The vfs helpers will take care of the rest.

Cc: <linux-unionfs@vger.kernel.org>
Tested-by: NGiuseppe Scrivano <gscrivan@redhat.com>
Reviewed-by: NAmir Goldstein <amir73il@gmail.com>
Signed-off-by: NChristian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>