Update git submodules

* Update docs/submodules/externalapi/nbi.git from branch 'master'
  to c4b865137354f422efb46f0f6efa846d1353239d
  - Merge "Initial draft of Frankfurt Release notes for RC0"
  - Initial draft of Frankfurt Release notes for RC0
    
    Issue-ID: EXTAPI-409
    
    Signed-off-by: aosull01 <adrian.osullivan@huawei.com>
    Change-Id: Icc190c8f1d5b10902f4676b425babc46807232dd
    
1 file changed