Update git submodules

Update git submodules

* Update docs/submodules/so/libs.git from branch 'elalto'
  to 59b4e783dc383539c0e0193d3a972a71b28d57f5
  - release the So/libs 1.5.1 artifacts

    Issue-ID: SO-2361

    Signed-off-by: seshukm <seshu.kumar.m@huawei.com>
    Change-Id: Ic238f718290aa4957c29efe121c599f551be621a

  - changed sprint number for build for issue so-2361

    earlier Addressed the error in retrieving subnets
    with SO Libs. Now chaging sprint number for build

    Issue-ID: SO-2361
    Signed-off-by: Ramesh Parthasarathy(rp6768)<ramesh.parthasarathy@att.com>
    Change-Id: I0fb8ba275229eebe0504176540f9f4b8e4574f9e

  - Addressed the error in retrieving subnets

    Addressed the error in retrieving subnets
    with SO Libs repository openstack SDK project

    Issue-ID: SO-2361
    Signed-off-by: Ramesh Parthasarathy(rp6768)<ramesh.parthasarathy@att.com>
    Change-Id: If54a8097ca16a266b075d3e5bfcf09157947087d