Update git submodules

Update git submodules

* Update docs/submodules/so.git from branch 'master'
  to 15e83aff4e9be045b5c36f865dc351f6e8f38238
  - Merge "Add SO Increase Action_category column width"
  - Add SO Increase Action_category column width

    Action_category column width in Controller_selection_category table
    is increased to accommodate activity categories like
    DistributeTrafficCheck which are longer than the column width.
    Issue-ID: SO-2185
    Signed-off-by: Bonkur, Venkat (vb8416) <vb8416@att.com>
    Change-Id: Ia5c813bfabfc95d4502c7ade4413672c64ad8ada