NFS: Fix up the declaration of nfs4_restart_rpc when NFSv4 not configured

Also rename it: it is used in generic code, and so should not have a 'nfs4'
prefix.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index d546c607..a28123b 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1216,7 +1216,7 @@
 				 */
 				argp->stable = NFS_FILE_SYNC;
 			}
-			nfs4_restart_rpc(task, server->nfs_client);
+			nfs_restart_rpc(task, server->nfs_client);
 			return -EAGAIN;
 		}
 		if (time_before(complain, jiffies)) {