Bump up portmap version to v0.8.7

[tnqn]

To fix a performance issue that portmap performs expensive iptables
operations even no portMappings are configured.

Upstream fix: containernetworking/plugins@877602d

Fixes #1499

[antrea-bot]

Thanks for your PR.
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[codecov-io]

Codecov Report

Merging #1534 (671a931) into master (6c1a913) will decrease coverage by 0.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1534      +/-   ##
==========================================
- Coverage   67.79%   67.65%   -0.14%     
==========================================
  Files         169      169              
  Lines       13503    13503              
==========================================
- Hits         9154     9136      -18     
- Misses       3407     3420      +13     
- Partials      942      947       +5     

Flag	Coverage Δ
integration-tests	45.64% <ø> (-0.07%)	⬇️
kind-e2e-tests	55.18% <ø> (-0.39%)	⬇️
unit-tests	41.17% <ø> (-0.08%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/apiserver/certificate/certificate.go	71.05% <0.00%> (-6.58%)	⬇️
pkg/controller/traceflow/controller.go	67.74% <0.00%> (-2.59%)	⬇️
pkg/ovs/openflow/ofctrl_bridge.go	70.35% <0.00%> (-1.59%)	⬇️
...ntroller/networkpolicy/networkpolicy_controller.go	82.97% <0.00%> (-0.73%)	⬇️

[tnqn]

/test-all

[tnqn]

@antoninbas I haven't updated the base image, want the PR get reviewed first. If it gets approval, could you help update the image and merge it to catch 0.10.2?

[tnqn]

/test-all

[antoninbas]

LGTM