Reintroduce cfg(dual_funding) for handling of open_channel2 messages

[dunxen]

There is still some work to be done here (like #3423) and it probably makes sense to release this (around v0.2) with the ability to open V2 channels too. This would also make our functional tests for dual-funding more complete.

[codecov]

Codecov Report

Attention: Patch coverage is 61.90476% with 8 lines in your changes missing coverage. Please review.

Project coverage is 90.17%. Comparing base (6e85a0d) to head (76608f7).
Report is 30 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/channel.rs	25.00%	3 Missing ⚠️
lightning/src/ln/channelmanager.rs	78.57%	3 Missing ⚠️
lightning/src/ln/peer_handler.rs	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3485      +/-   ##
==========================================
+ Coverage   89.71%   90.17%   +0.45%     
==========================================
  Files         130      129       -1     
  Lines      107625   114866    +7241     
  Branches   107625   114866    +7241     
==========================================
+ Hits        96553   103576    +7023     
- Misses       8672     8998     +326     
+ Partials     2400     2292     -108     

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[optout21]

Note: previously splicing branches used cfg(any(dual_funding, splicing)) for the dual funding code; if at that time dual_funding flag still exist, this will have to be done in #3444 .

[TheBlueMatt]

LGTM except we need to remove features.set_dual_fund_optional(); in provided_init_features too.

[dunxen]

Note: previously splicing branches used cfg(any(dual_funding, splicing)) for the dual funding code; if at that time dual_funding flag still exist, this will have to be done in #3444 .

So here I've been quite conservative and have only cfg flagged the parts (message handling) that are definitely just for dual-funding, and which splicing shouldn't be using. If that's not the case then would you mind introducing the any logic again?

[TheBlueMatt]

Thanks.

[TheBlueMatt]

Ha, this doesn't seem required :)

[dunxen]

Oh yup. Ended up removing the cfg flag in the branch...