refactor：manage libnetwork by subtree instead of submodule

[rudyfly]

Ⅰ. Describe what this PR did

Manage libnetwork by subtree instead of submodule.
Our libnetwork version is commit “09bc1d0839e32843828ced297ad634822a48c38b”， but we need to backport some patches to fix bugs, such as commit “7751e6f2f01243cca89a46a4e8553876c5d2698c”

Ⅱ. Does this pull request fix one issue?

NONE

Ⅲ. Describe how you did it

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

Signed-off-by: Rudy Zhang rudyflyzhang@gmail.com

[codecov-io]

Codecov Report

Merging #1135 into master will increase coverage by 1.66%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #1135      +/-   ##
=========================================
+ Coverage   15.54%   17.2%   +1.66%     
=========================================
  Files         172     165       -7     
  Lines        9739    8985     -754     
=========================================
+ Hits         1514    1546      +32     
+ Misses       8116    7327     -789     
- Partials      109     112       +3

Impacted Files	Coverage Δ
cli/inspect/inspector.go	53.52% <0%> (-19.62%)	⬇️
daemon/mgr/container_utils.go	56.19% <0%> (-1.85%)	⬇️
daemon/mgr/spec_linux.go	0% <0%> (ø)	⬆️
daemon/mgr/container_types.go	15.38% <0%> (ø)	⬆️
cli/inspect.go	0% <0%> (ø)	⬆️
cli/common_flags.go	0% <0%> (ø)	⬆️
cli/start.go	0% <0%> (ø)	⬆️
daemon/mgr/spec.go	0% <0%> (ø)	⬆️
cli/cli.go	0% <0%> (ø)	⬆️
daemon/mgr/system.go	0% <0%> (ø)	⬆️
... and 22 more

[yyb196]

LGTM