This commit adds signet support, which is a little bit silly/redundant for us :)
Was a surprisingly easy merge to handle, and hopefully in future Core is more
mindful of signed blocks when they are changing code architecture.
I had to change a couple lines of src/signet.cpp to add blank assets to the
CTxOuts and to find transaction input scriptWitnesses. No need to add any
other tx witness data (and the CAsset()s that I did add to make things compile
won't be used..) because signet will always have g_con_elementsmode off.
Introduce a new message `sendaddrv2` to signal support for ADDRv2.
Send the new message immediately after sending the `VERACK` message.
Add support for receiving and parsing ADDRv2 messages.
Send ADDRv2 messages (instead of ADDR) to a peer if he has
advertised support for it.
Co-authored-by: Carl Dong <contact@carldong.me>
