Update git submodules

Update git submodules

* Update docs/submodules/modeling/modelspec.git from branch 'master'
  to 51df70ea00e53e93f4fc337b3e9f4bfd28cf7b5d
  - Update enhanced service model

    Main changes are the ServiceProperties part, add 3GPP attributes in a
    new diagram"ServiceProperties", add a new attribute"maxAvailableNumber"
    in ServiceDescriptor, supplement stereotype in the model.

    Issue-ID: MODELING-104

    Change-Id: I6ff4961e4bc21b564b5a17ffa702dbd78ccfb186

    Change-Id: I6ff4961e4bc21b564b5a17ffa702dbd78ccfb186
    Signed-off-by: guochuyicmri <guochuyi@chinamobile.com>