[nrf fromtree] manifest: net: openthread: Regular openthread upmerge to 3873c6f.

Regular openthread upmerge to `3873c6fcd5a8a9dd01b71e8efe32ef5dc7923bb1`.

Signed-off-by: Przemyslaw Bida <[email protected]>
(cherry picked from commit 54d9fe3)

Author: Przemyslaw Bida

west.yml

@@ -301,7 +301,7 @@ manifest:
       revision: da78aea63159771956fe0c9263f2e6985b66e9d5
       path: modules/lib/open-amp
     - name: openthread
-      revision: 49c59ec519cc8b49dd58978d1bc80b7ae7ba88d0
+      revision: 3873c6fcd5a8a9dd01b71e8efe32ef5dc7923bb1
       path: modules/lib/openthread
     - name: percepio
       path: modules/debug/percepio