nfsd4: rename callback struct to cb_conn

I want to use the name for a struct that actually does represent a
single callback.

(Actually, I've never been sure it helps to a separate struct for the
callback information.  Some day maybe those fields could just be dumped
into struct nfs4_client.  I don't know.)

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
diff --git a/include/linux/nfsd/state.h b/include/linux/nfsd/state.h
index 8d882a3..563c367 100644
--- a/include/linux/nfsd/state.h
+++ b/include/linux/nfsd/state.h
@@ -88,7 +88,7 @@
 #define dl_fh           dl_recall.cbr_fh
 
 /* client delegation callback info */
-struct nfs4_callback {
+struct nfs4_cb_conn {
 	/* SETCLIENTID info */
 	u32                     cb_addr;
 	unsigned short          cb_port;
@@ -186,7 +186,7 @@
 	struct svc_cred		cl_cred; 	/* setclientid principal */
 	clientid_t		cl_clientid;	/* generated by server */
 	nfs4_verifier		cl_confirm;	/* generated by server */
-	struct nfs4_callback	cl_callback;    /* callback info */
+	struct nfs4_cb_conn	cl_cb_conn;     /* callback info */
 	atomic_t		cl_count;	/* ref count */
 	u32			cl_firststate;	/* recovery dir creation */