[17.12] Enable IPV6 config on Sandbox creation on live-restore

[thaJeztah]

Cherry-pick of #2043 for 17.12. I left out some unrelated commits from the PR

cherry picked from commit 76bfcb0, no conflicts

In sandbox creation we disable IPV6 config. But this causes problem in live-restore case
where all IPV6 configs are wiped out on running container. Hence extra check has been added
take care of this issue.

[codecov-io]

Codecov Report

Merging #2059 into bump_17.12 will decrease coverage by 0.14%.
The diff coverage is 100%.

@@              Coverage Diff               @@
##           bump_17.12    #2059      +/-   ##
==============================================
- Coverage       40.18%   40.04%   -0.15%     
==============================================
  Files             138      138              
  Lines           22135    22135              
==============================================
- Hits             8895     8863      -32     
- Misses          11935    11971      +36     
+ Partials         1305     1301       -4

Impacted Files	Coverage Δ
osl/namespace_linux.go	35.31% <100%> (+0.59%)	⬆️
networkdb/cluster.go	61.33% <0%> (-3.21%)	⬇️
endpoint_cnt.go	84.15% <0%> (-2.98%)	⬇️
ipam/store.go	70.58% <0%> (-2.95%)	⬇️
drivers/overlay/ov_network.go	2.32% <0%> (-2.33%)	⬇️
networkdb/delegate.go	74.26% <0%> (-0.74%)	⬇️
ipam/allocator.go	71.34% <0%> (-0.59%)	⬇️
iptables/iptables.go	58.51% <0%> (+0.7%)	⬆️

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[fcrisciani]

LGTM