NFS: Convert v4 into a module

This patch exports symbols needed by the v4 module.  In addition, I also
switch over to using IS_ENABLED() to check if CONFIG_NFS_V4 or
CONFIG_NFS_V4_MODULE are set.

The module (nfs4.ko) will be created in the same directory as nfs.ko and
will be automatically loaded the first time you try to mount over 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 1c825f3..12a31a9 100644
--- a/fs/nfs/nfs4super.c
+++ b/fs/nfs/nfs4super.c
@@ -332,7 +332,7 @@
 }
 
 
-int __init init_nfs_v4(void)
+static int __init init_nfs_v4(void)
 {
 	int err;
 
@@ -358,10 +358,15 @@
 	return err;
 }
 
-void exit_nfs_v4(void)
+static void __exit exit_nfs_v4(void)
 {
 	unregister_nfs_version(&nfs_v4);
 	unregister_filesystem(&nfs4_fs_type);
 	nfs4_unregister_sysctl();
 	nfs_idmap_quit();
 }
+
+MODULE_LICENSE("GPL");
+
+module_init(init_nfs_v4);
+module_exit(exit_nfs_v4);