NFS: make nfs_client_lock per net ns

This patch makes nfs_clients_lock allocated per network namespace. All items it
protects are already network namespace aware.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/netns.h

@@ -12,6 +12,7 @@ struct nfs_net {
 #ifdef CONFIG_NFS_V4
 	struct idr cb_ident_idr; /* Protected by nfs_client_lock */
 #endif
+	spinlock_t nfs_client_lock;
 };
 
 extern int nfs_net_id;