Support NAT functions in Antrea

[wenyingd]

Expand Antrea Openflow control interface to support NAT/SNAT/DNAT functions
in conntrack.

[antrea-bot]

Thanks for your PR.
Unit tests and code linters are run automatically every time the PR is updated.
E2e, conformance and network policy tests can only be triggered by a member of the vmware-tanzu organization. Regular contributors to the project should join the org.

The following commands are available:

• /test-e2e: to trigger e2e tests.
• /skip-e2e: to skip e2e tests.
• /test-conformance: to trigger conformance tests.
• /skip-conformance: to skip conformance tests.
• /test-networkpolicy: to trigger networkpolicy tests.
• /skip-networkpolicy: to skip networkpolicy tests.
• /test-all: to trigger all tests.
• /skip-all: to skip all tests.

These commands can only be run by members of the vmware-tanzu organization.

[wenyingd]

/test-all

[wenyingd]

/test-all

[wenyingd]

/test-networkpolicy