nfsd4: support BIND_CONN_TO_SESSION

Basic xdr and processing for BIND_CONN_TO_SESSION.  This adds a
connection to the list of connections associated with a session.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/include/linux/nfs4.h b/include/linux/nfs4.h
index 26afa30..a591893 100644
--- a/include/linux/nfs4.h
+++ b/include/linux/nfs4.h
@@ -65,6 +65,9 @@
 
 #define NFS4_CDFC4_FORE	0x1
 #define NFS4_CDFC4_BACK 0x2
+#define NFS4_CDFC4_BOTH 0x3
+#define NFS4_CDFC4_FORE_OR_BOTH 0x3
+#define NFS4_CDFC4_BACK_OR_BOTH 0x7
 
 #define NFS4_SET_TO_SERVER_TIME	0
 #define NFS4_SET_TO_CLIENT_TIME	1