[ Upstream commit b3e1eb8e ]

So that when it is unset, ie. '-1', userspace can see it
properly.
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>