Add iptables interface for implementing Egress

[tnqn]

For #1924

[tnqn]

/test-all

[codecov-io]

Codecov Report

Merging #1998 (80bcd88) into main (9b8440d) will decrease coverage by 0.11%.
The diff coverage is 5.66%.

@@            Coverage Diff             @@
##             main    #1998      +/-   ##
==========================================
- Coverage   65.39%   65.27%   -0.12%     
==========================================
  Files         197      197              
  Lines       17217    17268      +51     
==========================================
+ Hits        11259    11272      +13     
- Misses       4785     4824      +39     
+ Partials     1173     1172       -1     

Flag	Coverage Δ
kind-e2e-tests	56.42% <5.66%> (-0.10%)	⬇️
unit-tests	41.82% <0.00%> (-0.04%)	⬇️

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

Impacted Files	Coverage Δ
pkg/agent/util/iptables/iptables.go	38.88% <0.00%> (-7.34%)	⬇️
pkg/agent/route/route_linux.go	42.69% <9.09%> (-3.62%)	⬇️
...gent/controller/networkpolicy/status_controller.go	72.60% <0.00%> (-2.74%)	⬇️
...ntroller/networkpolicy/networkpolicy_controller.go	70.12% <0.00%> (-1.63%)	⬇️
pkg/agent/openflow/client.go	67.19% <0.00%> (+0.52%)	⬆️
pkg/agent/cniserver/pod_configuration.go	54.68% <0.00%> (+0.78%)	⬆️
pkg/controller/networkpolicy/tier.go	52.50% <0.00%> (+5.00%)	⬆️
pkg/monitor/controller.go	57.57% <0.00%> (+6.06%)	⬆️
pkg/agent/flowexporter/flowrecords/flow_records.go	67.34% <0.00%> (+6.12%)	⬆️
pkg/apiserver/certificate/certificate.go	76.71% <0.00%> (+6.84%)	⬆️

[tnqn]

/test-all

[tnqn]

/test-windows-conformance