Update UTCP to support fragmenting packets on UDP style channels.

[meshlink] / src / utcp

diff --git a/src/utcp b/src/utcp
index 134cccee1441033ad5bcb736a689a3a7481886d8..a7d31e61566f0d2e6cb0821fcdaf74ccfc1f8f64 160000 (submodule)
--- a/src/utcp
+++ b/src/utcp
@@ -1 +1 @@
-Subproject commit 134cccee1441033ad5bcb736a689a3a7481886d8
+Subproject commit a7d31e61566f0d2e6cb0821fcdaf74ccfc1f8f64