[roll] Roll fuchsia [netstack3] Support PROBE_WAIT for IPv4 DAD

Wait for up to 1 second before starting to send ARP probes for IPv4
Addresses that are undergoing Address Conflict Detection.

Original-Bug: 42077260
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1275707
Original-Revision: b421ec319973d4fb002da93bb5e3b649c7e7d36c
GitOrigin-RevId: 651ccaaaaa246d12c8ef273c3bd64f39366545c9
Change-Id: Ic2d5d4010d4c606eac6b0ea29024f2c571f20fef
diff --git a/stem b/stem
index 3bdec26..cd6a1e7 100644
--- a/stem
+++ b/stem
@@ -8,7 +8,7 @@
              root=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="a4b716f9b845b95f108a98e8d9b33d8b6607ae3c"
+             revision="b421ec319973d4fb002da93bb5e3b649c7e7d36c"
              />
   </imports>
   <projects>