NFSv4 only print the label when its queried

[ Upstream commit 2c52c8376db7160a1dd8a681c61c9258405ef143 ]

When the bitmask of the attributes doesn't include the security label,
don't bother printing it. Since the label might not be null terminated,
adjust the printing format accordingly.

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>