NFS: Create a try_mount rpc op

I'm already looking up the nfs subversion in nfs_fs_mount(), so I have
easy access to rpc_ops that used to be difficult to reach.  This allows
me to set up a different mount path for NFS v2/3 and NFS v4.

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/nfs4super.c b/fs/nfs/nfs4super.c
index 8a50557..9384f66 100644
--- a/fs/nfs/nfs4super.c
+++ b/fs/nfs/nfs4super.c
@@ -226,7 +226,8 @@
 }
 
 struct dentry *nfs4_try_mount(int flags, const char *dev_name,
-			 struct nfs_mount_info *mount_info)
+			      struct nfs_mount_info *mount_info,
+			      struct nfs_subversion *nfs_mod)
 {
 	char *export_path;
 	struct vfsmount *root_mnt;