Hold off on tagging 28.0

[JeremyRand]

@domob1812 please hold off on tagging nc28.0 until I can make sure a few potential blockers are dealt with.

[JeremyRand]

Potential blockers:

• Default IP and onion P2P ports conflict with each other, and with Bitcoin Core default onion P2P port #545
• Making sure Guix builds succeed and are reproducible.
• Asking our QA team to briefly try the Guix binaries.

[JeremyRand]

Other potential blockers:

• Making sure Guix builds on ppc64le are reproducible with x86_64.
• Update the seed node list.

[JeremyRand]

@domob1812 can you cherry-pick #553 and #557 to the 28.x branch?

Other remaining blockers for tagging 28.0:

• Making sure Guix builds on ppc64le are reproducible with x86_64.
  • This looks like there was a regression upstream between 27.x and 28.x. I've reported a bug upstream today. I will re-evaluate whether I want this to block a release once upstream responds, and once I talk with our other Guix builders.
• Making sure Guix builds succeed and are reproducible.
• Asking our QA team to briefly try the Guix binaries.
• Update the seed node list (including mainnet DNS seeds).

[domob1812]

Done the backports of #553 and #557.

[JeremyRand]

Based on discussion with upstream, I'm not going to block a 28.0 release on ppc64le build arch reproducibility. We will try to have this sorted out for 29.0.

Given the above, Robert and Rose are handling Guix builds for the 28.x cycle. Their binaries are confirmed reproducible.

Our QA team has looked at the 28.x branch. A few issues were noted, but none of them are worth blocking a 28.0 tag. Updating the seed nodes is also not worth blocking a 28.0 tag.

@domob1812 You are free to tag 28.0. Please do so within the next 24 hours if it is possible, so that Robert and Rose can do their Guix builds of the tag, and I can publish the release, before everyone departs for 38C3 at the beginning of next week.