Change Details

`buildLocalChallenge` is extracted from `sendHello` and `buildRemoteChallenge` will be used in D9327 to check the AVAHELLO message sent by a peer.

`buildLocalSighash` is extracted from `sendHello` and `buildRemoteSighash` will be used in D9327 to check the AVAHELLO message sent by a peer.

`buildLocalChallenge`Sighash` is extracted from `sendHello` and `buildRemoteChallenge`Sighash` will be used in D9327 to check the AVAHELLO message sent by a peer.