sunrpc: Add xprt after nfs4_test_session_trunk()

Multipathing: In case of NFSv3, rpc_clnt_test_and_add_xprt() adds
the xprt to xprt switch (i.e. xps) if rpc_call_null_helper() returns
success. But in case of NFSv4.1, it needs to do EXCHANGEID to verify
the path along with check for session trunking.

Add the xprt in nfs4_test_session_trunk() only when
nfs4_detect_session_trunking() returns success. Also release refcount
hold by rpc_clnt_setup_test_and_add_xprt().

Signed-off-by: Santosh kumar pradhan <santoshkumar.pradhan@wdc.com>
Tested-by: Suresh Jayaraman <suresh.jayaraman@wdc.com>
Reported-by: Aditya Agnihotri <aditya.agnihotri@wdc.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
index 993378a..06ac3d9a 100644
--- a/fs/nfs/nfs4_fs.h
+++ b/fs/nfs/nfs4_fs.h
@@ -65,7 +65,8 @@ struct nfs4_minor_version_ops {
 			nfs4_stateid *, const struct cred *);
 	struct nfs_seqid *
 		(*alloc_seqid)(struct nfs_seqid_counter *, gfp_t);
-	int	(*session_trunk)(struct rpc_clnt *, struct rpc_xprt *, void *);
+	void	(*session_trunk)(struct rpc_clnt *clnt,
+			struct rpc_xprt *xprt, void *data);
 	const struct rpc_call_ops *call_sync_ops;
 	const struct nfs4_state_recovery_ops *reboot_recovery_ops;
 	const struct nfs4_state_recovery_ops *nograce_recovery_ops;