We rename `ChanUpdateOptionMaxHtlc` to `ChanUpdateRequiredMaxHtlc`
as with the latest changes it is now required.
Similarly, rename `validateOptionalFields` to
`ValidateChannelUpdateFields`, export it to use it in a later commit.
This commit was previously split into the following parts to ease
review:
- 2d746f68: replace imports
- 4008f0fd: use ecdsa.Signature
- 849e33d1: remove btcec.S256()
- b8f6ebbd: use v2 library correctly
- fa80bca9: bump go modules
This commits adds the devrpc package which implements a subserver that
adds clean separation for RPC calls useful for development and
debugging. This subserver is only compiled in if the dev tag is set.
Furthermore the commit adds the devrpc.ImportGraph call which can
import a graph dump obtained from another node by calling DescribeGraph.
Since the graph dump does not include the auth proofs, the imported
channels will be considered private.
