Fix retransmission timeout calculation in UTCP.

This could result in unnecessary retransmissions and lower throughput of
channels.

diff --git a/src/utcp b/src/utcp
index 25675cca79330f968b3fb106793a5265615f4df7..eb85ec4ae5f32102430e0622e3855aaba110c032 160000 (submodule)
--- a/src/utcp
+++ b/src/utcp
@@ -1 +1 @@
-Subproject commit 25675cca79330f968b3fb106793a5265615f4df7
+Subproject commit eb85ec4ae5f32102430e0622e3855aaba110c032