Add a new min-funding config parameter for private channels

[remyers]

Add the ability to set a different min-funding limit for private and public channels. See issue "Private channels should have their own dedicated 'min-funding-satoshis' setting" #2077.

If channel.private.enable-alt = true then the channel.private.min-funding-satoshis value will be used for private channels, otherwise the channel.min-funding-satoshis will be used for both public and private channels.

A few questions:

• previous min-funding-satoshis tests compared assert(error.toAscii === Error(...).toAscii) while other tests in WaitForOpenChannelStateSpec left off the .toAscii. Is there a reason to use the .toAscii in the assert here?
• Issue 2077 mentioned we should document that users should not set unsafely low min-funding limits for private channels. Only if users set their public channels to have higher limits then they might allow private channels with a lower, but still safe, min-funding-satoshis. Should I add documentation to that effect in docs\Configure.md ? or in the release notes ?

[remyers]

My rational for the channel.private.enable-alt is that when people upgrade their node it should default to have the same min-funding behavior as before. If we just added a new setting for private channels then it would use whatever default was in the reference.conf and that would potentially be very different than what the user expects their private channels to use.

I'm not completely happy with the enable-alt as the name for that parameters - open to suggestions.

[codecov-commenter]

Codecov Report

Merging #2203 (6534977) into master (f3c6c78) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2203      +/-   ##
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- Coverage   83.89%   83.88%   -0.02%     
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  Files         186      186              
  Lines       13937    13940       +3     
  Branches      545      580      +35     
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  Hits        11693    11693              
- Misses       2244     2247       +3     

Impacted Files	Coverage Δ
...re/src/main/scala/fr/acinq/eclair/NodeParams.scala	92.77% <100.00%> (+0.05%)	⬆️
...c/main/scala/fr/acinq/eclair/channel/Channel.scala	87.81% <100.00%> (+0.08%)	⬆️
...c/main/scala/fr/acinq/eclair/channel/Helpers.scala	94.97% <100.00%> (ø)
...ala/fr/acinq/eclair/balance/ChannelsListener.scala	93.10% <0.00%> (-3.45%)	⬇️
...clair/channel/publish/ReplaceableTxPublisher.scala	72.84% <0.00%> (-1.33%)	⬇️
...main/scala/fr/acinq/eclair/io/PeerConnection.scala	85.60% <0.00%> (-0.76%)	⬇️
...cala/fr/acinq/eclair/crypto/TransportHandler.scala	90.76% <0.00%> (+0.54%)	⬆️

[thomash-acinq]

I understand your rationale for channel.private.enable-alt but I really don't like the result.
An alternative would be to rename min-funding-satoshis to min-public-funding-satoshis and add a deprecation message for min-funding-satoshis, that way everyone using this parameter will see the message and will be forced to manually change it.

[pm47]

@thomash-acinq beat me to it, indeed it's the way to go:

eclair/eclair-core/src/main/scala/fr/acinq/eclair/NodeParams.scala

Line 173 in f3c6c78

val deprecatedKeyPaths = Map(

[remyers]

I understand your rationale for channel.private.enable-alt but I really don't like the result. An alternative would be to rename min-funding-satoshis to min-public-funding-satoshis and add a deprecation message for min-funding-satoshis, that way everyone using this parameter will see the message and will be forced to manually change it.

I agree. As long as we mention both new options in the deprecation message that should ensure they know to set both the public and private min funding values.

[thomash-acinq]

I don't think these comments are really helpful. Larger channels are more attractive but that doesn't have anything to do with the minimum we set here, a small channel is more attractive than no channel.

[remyers]

Removed them in 6534977. Sounds like its too nuanced to explain in comments.

[thomash-acinq]

I've just remembered about the release notes, can you update them too?

[pm47]

Also, for PR names and squashed commit messages please use a short sentence starting by a verb with an uppercase.