Update git submodules

Update git submodules

* Update docs/submodules/externalapi/nbi.git from branch 'master'
  to 6413a21daa01e4ff25fad4f49bc35b01cb98a1a7
  - Merge "Improve security release notes"
  - Improve security release notes

    In order to provide users with more details of project's state in
    terms of security let's divide the security release notes into three
    sections:

    - Fixed Security Issues
      Contains a list of security fixes merged during this
      release (especially those reported via OJSI tickets).

    - Known Security Issues
      Contains a list of vulnerabilities detected in project during
      release which have not been fixed yet and thus should be mitigated
      by the user.

    - Known Vulnerabilities in Used Modules
      Contains information about NexusIQ scan results

    Issue-ID: SECCOM-238
    Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
    Change-Id: I07a057dd5bdec7a2d3ad42be854faa9c8abd38e0