Update rdns.

diff --git a/src/rdns b/src/rdns
index 8d80ac78cf6436c077804dd0972866a5bd55732f..a21b4c0afc2c4bd7a2a16fbd6ba05033c926f6c2 160000 (submodule)
--- a/src/rdns
+++ b/src/rdns
@@ -1 +1 @@
-Subproject commit 8d80ac78cf6436c077804dd0972866a5bd55732f
+Subproject commit a21b4c0afc2c4bd7a2a16fbd6ba05033c926f6c2