fedfsd: xp_auth field was moved

From: Chuck Lever <chuck.lever@oracle.com>

A recent version of libtirpc changed an undocumented interface.
Add some compatibility measures.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 src/fedfsd/gss.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/fedfsd/gss.c b/src/fedfsd/gss.c
index c63f42f..f762466 100644
--- a/src/fedfsd/gss.c
+++ b/src/fedfsd/gss.c
@@ -175,6 +175,10 @@ fedfsd_get_gss_cred(struct svc_req *rqstp)
 {
 	SVCAUTH *auth;
 
+#if defined(SVC_XP_AUTH)
+	auth = &SVC_XP_AUTH(rqstp->rq_xprt);
+#else
 	auth = rqstp->rq_xprt->xp_auth;
+#endif
 	return svcauth_gss_get_principal(auth);
 }