Disallow empty port list for ANP peers.

[npinaeva]

Based on discussion #247
Zero-length port list is different from the nil port list, and it means do not match any port, which makes that peer not matching any traffic.
This is confusing and is more of an accident than an intention.
Closes #247

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[aojea]

@danwinship don't you bump the versions for these changes? v1alpha2?

[danwinship]

/approve

@danwinship don't you bump the versions for these changes? v1alpha2?

pfft. YOLO!

Yeah, it's technically an API break, but it's alpha. I guess people who are shipping this alpha API to customers (meaningful glance) will have to decide whether or not to ship the break.

(leaving un-lgtm'ed to give others a chance to comment)

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[APPROVALNOTIFIER] This PR is APPROVED

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[npinaeva]

/retest

[npinaeva]

had to rebase to fix CI

[aojea]

I see, ok, let me know when you have planned a release to update the network policies,

[aojea]

we may want to do a release before kubecon, and then freeze there, otherwise we loose credibility too

[aojea]

we can break between alpha minors

[danwinship]

/lgtm