nfsd4: move principal name into svc_cred

Instead of keeping the principal name associated with a request in a
structure that's private to auth_gss and using an accessor function,
move it to svc_cred.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index cff3940..970659d 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -343,7 +343,7 @@
 int
 check_gss_callback_principal(struct nfs_client *clp, struct svc_rqst *rqstp)
 {
-	char *p = svc_gss_principal(rqstp);
+	char *p = rqstp->rq_cred.cr_principal;
 
 	if (rqstp->rq_authop->flavour != RPC_AUTH_GSS)
 		return 1;