Work around LND bug 6039

[TheBlueMatt]

LND hasn't properly handled shutdown messages ever, and force-closes any time we send one while HTLCs are still present. The issue is tracked at
lightningnetwork/lnd#6039 and has had multiple patches to fix it but none so far have managed to land upstream. The issue appears to be very low priority for the LND team despite being marked "P1".

We're not going to bother handling this in a sensible way, instead simply repeated the Shutdown message on repeat until morale improves.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.66% 🎉

Comparison is base (d4ad826) 90.40% compared to head (b149279) 91.07%.
Report is 7 commits behind head on main.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2507      +/-   ##
==========================================
+ Coverage   90.40%   91.07%   +0.66%     
==========================================
  Files         106      106              
  Lines       56268    63310    +7042     
  Branches    56268    63310    +7042     
==========================================
+ Hits        50868    57657    +6789     
- Misses       5400     5653     +253     

Files Changed	Coverage Δ
lightning/src/events/mod.rs	47.95% <100.00%> (+5.43%)	⬆️
lightning/src/ln/channel.rs	91.93% <100.00%> (+2.46%)	⬆️
lightning/src/ln/channelmanager.rs	89.64% <100.00%> (+4.11%)	⬆️
lightning/src/ln/msgs.rs	85.35% <100.00%> (ø)
lightning/src/ln/shutdown_tests.rs	98.52% <100.00%> (+0.06%)	⬆️

... and 9 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[wpaulino]

I'm not too happy with just continuously re-sending shutdown, but doing anything smarter is likely not worth the complexity. Hopefully they can get this fixed when implementing the new co-op close.

[TheBlueMatt]

Yea, its an absolutely awful solution, but I really dont want to write more crap just for LND. We might consider also sending a warning message just to say "hey, you're broken, please upgrade", but also didn't bother. I could add that if we want.

[dunxen]

We might consider also sending a warning message just to say "hey, you're broken, please upgrade", but also didn't bother. I could add that if we want.

Might be worth it out of generosity, but not a blocker imho.

[TheBlueMatt]

Alright, fair, I added a warning message push.