NFSD: hide unused svcxdr_dupstr()

There is now only one caller left for svcxdr_dupstr() and this is inside
of an #ifdef, so we can get a warning when the option is disabled:

fs/nfsd/nfs4xdr.c:241:1: error: 'svcxdr_dupstr' defined but not used [-Werror=unused-function]

This changes the remaining caller to use a nicer IS_ENABLED() check,
which lets the compiler drop the unused code silently.

Fixes: e40d99e6183e ("NFSD: Clean up symlink argument XDR decoders")
Suggested-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4xdr.c

@@ -455,8 +455,8 @@ nfsd4_decode_fattr(struct nfsd4_compoundargs *argp, u32 *bmval,
 	}
 
 	label->len = 0;
-#ifdef CONFIG_NFSD_V4_SECURITY_LABEL
-	if (bmval[2] & FATTR4_WORD2_SECURITY_LABEL) {
+	if (IS_ENABLED(CONFIG_NFSD_V4_SECURITY_LABEL) &&
+	    bmval[2] & FATTR4_WORD2_SECURITY_LABEL) {
 		READ_BUF(4);
 		len += 4;
 		dummy32 = be32_to_cpup(p++); /* lfs: we don't use it */
@@ -476,7 +476,6 @@ nfsd4_decode_fattr(struct nfsd4_compoundargs *argp, u32 *bmval,
 		if (!label->data)
 			return nfserr_jukebox;
 	}
-#endif
 	if (bmval[2] & FATTR4_WORD2_MODE_UMASK) {
 		if (!umask)
 			goto xdr_error;