Fix random underflow.

Fixes: 63335997
Test: Boot a couple of Fugu's warm and cold and observe via top
      that mdns task is not hogging CPU cycles.

Change-Id: Ia03114fc282ee1484bb782bce614073e93e2490a
(cherry picked from commit 448cff811f242f271f2d473939f679c89f151758)
1 file changed