ceph: reset iov_len when discarding cap release messages

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Sage Weil <sage@inktank.com>
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 4d29203..ddbd590 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -1391,6 +1391,7 @@
 	num = le32_to_cpu(head->num);
 	dout("discard_cap_releases mds%d %p %u\n", session->s_mds, msg, num);
 	head->num = cpu_to_le32(0);
+	msg->front.iov_len = sizeof(*head);
 	session->s_num_cap_releases += num;
 
 	/* requeue completed messages */