Update git submodules

* Update docs/submodules/armband from branch 'stable/danube'
  - Append offloading modes and MTU to interfaces

    Select information regarding offloading modes
    and MTU and append it to the interface properties key,
    for each defined interface.
    Revert previous related commit, due to incompatibility
    with dea parsing and interpreting methods.

    JIRA: https://jira.opnfv.org/browse/ARMBAND-199
    JIRA: https://jira.opnfv.org/browse/ARMBAND-251
    JIRA: https://jira.opnfv.org/browse/ARMBAND-253

    Change-Id: I6227ba6b5fed07b417b13d3b7a4e07f63a7a2383
    Signed-off-by: Catalina Focsa <catalina.focsa@enea.com>

diff --git a/docs/submodules/armband b/docs/submodules/armband
index b11ee1d..531f189 160000 (submodule)
--- a/docs/submodules/armband
+++ b/docs/submodules/armband
@@ -1 +1 @@
-Subproject commit b11ee1d7c13dd3ba42c36d7f73f99ac097ed534d
+Subproject commit 531f18918366d02a8a1c86576556e02eee59e8c9