Update UTCP to fix RTT measurements.

diff --git a/src/utcp b/src/utcp
index a7d31e61566f0d2e6cb0821fcdaf74ccfc1f8f64..a777291946071f7c30a439d26aa061d472f1024c 160000 (submodule)
--- a/src/utcp
+++ b/src/utcp
@@ -1 +1 @@
-Subproject commit a7d31e61566f0d2e6cb0821fcdaf74ccfc1f8f64
+Subproject commit a777291946071f7c30a439d26aa061d472f1024c