NFSv4.2: another fix for listxattr

NFSv4.2: another fix for listxattr

[ Upstream commit 9acb237deff7667b0f6b10fe6b1b70c4429ea049 ]

Currently, when the server supports NFS4.1 security labels then
security.selinux label in included twice. Instead, only add it
when the server doesn't possess security label support.

Fixes: 243fea134633 ("NFSv4.2: fix listxattr to return selinux security label")
Signed-off-by: Olga Kornievskaia <okorniev@redhat.com>
Link: https://lore.kernel.org/r/20250722205641.79394-1-okorniev@redhat.com
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>