Update git submodules

Update git submodules

* Update docs/submodules/clover from branch 'master'
  - Merge "CLOVER-43: Initial commit for Clovisor"
  - CLOVER-43: Initial commit for Clovisor

    Part of Clover's initial task (during project proposal) is to explore
    cloud native network tracing tools. Clover the project proposes
    Clovisor as a way for Clover to use the IOvisor
    (https://www.iovisor.org/) to perform network tracing. This is the first
    commit of this module

    Please note that the BPF code used in this commit were only tested with
    Linux kernel 4.14+ --- hence, if ubuntu is used, and one prefers LTS,
    the requirement is 18.04+

    A different patch will track the redis and k8s API server watcher code

    Also, a design doc will be added in the future (TBD)

    Signed-off-by: Stephen Wong <stephen.kf.wong@gmail.com>
    Change-Id: I30d9f9d474b8703097c470d39628e86bc788f9b6