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>
diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index dfd764b..e56e846 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -292,7 +292,9 @@
 {
 	if (req->wb_context->cred != prev->wb_context->cred)
 		return false;
-	if (req->wb_lock_context->lockowner != prev->wb_lock_context->lockowner)
+	if (req->wb_lock_context->lockowner.l_owner != prev->wb_lock_context->lockowner.l_owner)
+		return false;
+	if (req->wb_lock_context->lockowner.l_pid != prev->wb_lock_context->lockowner.l_pid)
 		return false;
 	if (req->wb_context->state != prev->wb_context->state)
 		return false;