Update pre-HTLC DataLossProtect to match new spec changes

This was the way DataLossProtect was originally written, however it
didn't match other implementations at the time during testing. It
turns out, other implementations didn't agree with each other
anyway (depending on the exact timeline), so the spec was clarified
somewhat in lightning/bolts#550
. This updates us to be in line with the new guidance and appears
to solve out-of-sync issues in testing.

Author: TheBlueMatt

lightning/src/ln/channel.rs

@@ -3444,10 +3444,10 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 				my_current_per_commitment_point: PublicKey::from_secret_key(&self.secp_ctx, &self.build_local_commitment_secret(self.cur_local_commitment_transaction_number + 1))
 			})
 		} else {
-			log_debug!(self, "We don't seen yet any revoked secret, if this channnel has already been updated it means we are fallen-behind, you should wait for other peer closing");
+			log_info!(self, "Sending a data_loss_protect with no previous remote per_commitment_secret");
 			OptionalField::Present(DataLossProtect {
 				your_last_per_commitment_secret: [0;32],
-				my_current_per_commitment_point: PublicKey::from_secret_key(&self.secp_ctx, &self.build_local_commitment_secret(self.cur_local_commitment_transaction_number))
+				my_current_per_commitment_point: PublicKey::from_secret_key(&self.secp_ctx, &self.build_local_commitment_secret(self.cur_local_commitment_transaction_number + 1))
 			})
 		};
 		msgs::ChannelReestablish {