Update git submodules

* Update docs/submodules/releng from branch 'master'
  to d24f28c142db7ab4bfd6a5bc000c76e85ae2994a
  - Fully remove sig_network_serial

    Change-Id: I1219f35d0e192ff898f15d44857a858c19803faf
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 2714395..d24f28c 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 2714395a2a485fbbdb19b8f77bf63b3b8ead1594
+Subproject commit d24f28c142db7ab4bfd6a5bc000c76e85ae2994a