Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "[VSPERF] Added releases tag and release-notes URL"
  - [VSPERF] Added releases tag and release-notes URL

    Updated the following in vswitchperf.yaml
    1. Added releases: opnfv-6.0.0
    2. updated the SHA1 for stable/fraser
    3. Added release-notes

    Moved URL to new line to overcome the line-length limit
    Patch-set3: Restored the git tag of stable/fraser to the original

    Change-Id: Ie41f874a92869c5e9225881cd8501b4d4ba7c5c4
    Signed-off-by: Sridhar K. N. Rao <sridhar.rao@spirent.com>