NFS: Background flush should not be low priority

Background flush is needed in order to satisfy the global page limits.
Don't subvert by reducing the priority.
This should also address a write starvation issue that was reported by
Neil Brown.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 7b93164..7a4fe7d 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -247,8 +247,6 @@
 		return FLUSH_HIGHPRI | FLUSH_STABLE;
 	if (wbc->sync_mode == WB_SYNC_ALL)
 		ret = FLUSH_COND_STABLE;
-	if (wbc->for_kupdate || wbc->for_background)
-		ret |= FLUSH_LOWPRI;
 	return ret;
 }