Electrum: stop spamming logs

[sstone]

Connection errors that happen before a proper handshake (i.e exchange of "version" messages) has been completed are now logged as "debug". Errors that are not sent by our master Electrum server are also logged as debug.
This greatly reduces the amount of connection-related logs, especially on testnet, and users will still be able to tell if they have connection issues (tested with eclair-mobile and Phoenix).

The last commit updates our electrum checkpoints.

[t-bast]

LGTM, how do we review/validate the updated checkpoints?

[sstone]

The checkpoints are imported from Electrum (we use the exact same format), these come from spesmilo/electrum@fc80f7a

They are block hashes and difficulty targets taken every 2016 blocks (which is the difficulty adjustment period). They can be checked manually:

• there is one item every 2016 blocks
• block height should be N*2016 - 1
• the bits field of the next block should match the checkpoint's nexbits field (on mainnet only, checking this on testnet is a PITA)

For example the last item on our mainnet checkpoint is:

    [
        "00000000000000000006da92c61b6b63ea910be27cab5fd951137105314f2969",
        1740794600224838465872409004248364704712181251938713600
    ]

The corresponding block header is:

{
  "hash": "00000000000000000006da92c61b6b63ea910be27cab5fd951137105314f2969",
  "confirmations": 12754,
  "height": 618911,
  "version": 536870912,
  "versionHex": "20000000",
  "merkleroot": "617f1010c9e0b37173d76e2eb6e57b0e3479b5c192744639260f931c978ae7aa",
  "time": 1582619298,
  "mediantime": 1582615830,
  "nonce": 544318282,
  "bits": "17121ad4",
  "difficulty": 15546745765529.37,
  "chainwork": "00000000000000000000000000000000000000000d037486edebab30d3c6c0e0",
  "nTx": 2605,
  "previousblockhash": "00000000000000000005c645e873072ab04834ba30eedfb192af5347ff2ffd14",
  "nextblockhash": "00000000000000000003fa80fb38019a948f5eec1e6e285a8d1eaec21d197c5f"
}

And the next bits field can be computed as (with the scala console for example):

scala> fr.acinq.bitcoin.encodeCompact(new java.math.BigInteger("1740794600224838465872409004248364704712181251938713600")).toHexString
res0: String = 17122cbc

We can check that it matches the bits field of the block that comes just after our checkoint hash:

bitcoin-cli getblockheader `bitcoin-cli getblockhash 618912`
{
  "hash": "00000000000000000003fa80fb38019a948f5eec1e6e285a8d1eaec21d197c5f",
  "confirmations": 12754,
  "height": 618912,
  "version": 536879104,
  "versionHex": "20002000",
  "merkleroot": "1f320d5b00e7cae0187abafcab2a0babd8490b03b37c3f2f375151f6d6a18f2d",
  "time": 1582619322,
  "mediantime": 1582616324,
  "nonce": 1684026233,
  "bits": "17122cbc",
  "difficulty": 15486913440292.87,
  "chainwork": "00000000000000000000000000000000000000000d03829ccffaf764ff73fbe9",
  "nTx": 2587,
  "previousblockhash": "00000000000000000006da92c61b6b63ea910be27cab5fd951137105314f2969",
  "nextblockhash": "0000000000000000000afbc86127bb1784a799beebe56ecd51361b8c4c519a42"
}