[roll] Roll fuchsia [netstack3] Avoid Task::spawn in Netstack::serve()

After this change, fasync::Task is still spawned in udp sockets and in
test code.

Test: No behavior change
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/580565
Original-Revision: e6dd9fbdf0c9aa9d25eafdc2979521e5e4e12b28
GitOrigin-RevId: ef4d534d05a4363d8238ee145d2de75235d91861
Change-Id: I667c988c1e0eead53b79b156b293d44a030a06ce
diff --git a/stem b/stem
index 4c1d8c1..175a576 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="5da00d05c6d0c42a6f745fa7327148db6bfa79c3"/>
+             revision="e6dd9fbdf0c9aa9d25eafdc2979521e5e4e12b28"/>
   </projects>
   <hooks>
     <hook name="install-environment"