NFS: Clean up helper function nfs4_select_rw_stateid()

We want to be able to pass on the information that the page was not
dirtied under a lock. Instead of adding a flag parameter, do this
by passing a pointer to a 'struct nfs_lock_owner' that may be NULL.

Also reuse this structure in struct nfs_lock_context to carry the
fl_owner_t and pid_t.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/nfs_fs.h

@@ -81,12 +81,16 @@ struct nfs_access_entry {
 	int			mask;
 };
 
+struct nfs_lockowner {
+	fl_owner_t l_owner;
+	pid_t l_pid;
+};
+
 struct nfs_lock_context {
 	atomic_t count;
 	struct list_head list;
 	struct nfs_open_context *open_context;
-	fl_owner_t lockowner;
-	pid_t pid;
+	struct nfs_lockowner lockowner;
 };
 
 struct nfs4_state;