NFS: Ensure the NFS_CAP_SECURITY_LABEL capability is set when appropriate

Commit ce62b11 ("NFS: Split attribute support out from the server
capabilities") removed the logic from _nfs4_server_capabilities() that
sets the NFS_CAP_SECURITY_LABEL capability based on the presence of
FATTR4_WORD2_SECURITY_LABEL in the attr_bitmask of the server's response.
Now NFS_CAP_SECURITY_LABEL is never set, which breaks labelled NFS.

This was replaced with logic that clears the NFS_ATTR_FATTR_V4_SECURITY_LABEL
bit in the newly added fattr_valid field based on the absence of
FATTR4_WORD2_SECURITY_LABEL in the attr_bitmask of the server's response.
This essentially has no effect since there's nothing looks for that bit
in fattr_supported.

So revert that part of the commit, but adding the logic that sets
NFS_CAP_SECURITY_LABEL near where the other capabilities are set in
_nfs4_server_capabilities().

Fixes: ce62b11 ("NFS: Split attribute support out from the server capabilities")
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

Author: scottmayhew

fs/nfs/nfs4proc.c

@@ -3878,6 +3878,10 @@ static int _nfs4_server_capabilities(struct nfs_server *server, struct nfs_fh *f
 			server->caps |= NFS_CAP_HARDLINKS;
 		if (res.has_symlinks != 0)
 			server->caps |= NFS_CAP_SYMLINKS;
+#ifdef CONFIG_NFS_V4_SECURITY_LABEL
+		if (res.attr_bitmask[2] & FATTR4_WORD2_SECURITY_LABEL)
+			server->caps |= NFS_CAP_SECURITY_LABEL;
+#endif
 		if (!(res.attr_bitmask[0] & FATTR4_WORD0_FILEID))
 			server->fattr_valid &= ~NFS_ATTR_FATTR_FILEID;
 		if (!(res.attr_bitmask[1] & FATTR4_WORD1_MODE))
@@ -3898,10 +3902,6 @@ static int _nfs4_server_capabilities(struct nfs_server *server, struct nfs_fh *f
 			server->fattr_valid &= ~NFS_ATTR_FATTR_CTIME;
 		if (!(res.attr_bitmask[1] & FATTR4_WORD1_TIME_MODIFY))
 			server->fattr_valid &= ~NFS_ATTR_FATTR_MTIME;
-#ifdef CONFIG_NFS_V4_SECURITY_LABEL
-		if (!(res.attr_bitmask[2] & FATTR4_WORD2_SECURITY_LABEL))
-			server->fattr_valid &= ~NFS_ATTR_FATTR_V4_SECURITY_LABEL;
-#endif
 		memcpy(server->attr_bitmask_nl, res.attr_bitmask,
 				sizeof(server->attr_bitmask));
 		server->attr_bitmask_nl[2] &= ~FATTR4_WORD2_SECURITY_LABEL;