tapchannel: send funding err to remote on failure

If we fail to fund the channel (for example because we don't have enough
BTC or asset funds), we inform the remote about it, so they can remove
the pending channel from their in-memory state and allow us to try
again.

Author: guggero

tapchannel/aux_funding_controller.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	crand "crypto/rand"
+	"errors"
 	"fmt"
 	"io"
 	"net/url"
@@ -1442,6 +1443,19 @@ func (f *FundingController) processFundingReq(fundingFlows fundingFlowIndex,
 					uErr)
 			}
 
+			// If anything went wrong during the funding process,
+			// the remote side might have an in-memory state and
+			// wouldn't allow us to try again within the next 10
+			// minutes (due to only one pending channel per peer
+			// default value). To avoid running into this issue, we
+			// make sure to inform the remote about us aborting the
+			// channel. We don't send them the actual error though,
+			// that would give away too much information.
+			f.cfg.ErrReporter.ReportError(
+				fundReq.ctx, fundReq.PeerPub, tempPID,
+				errors.New("internal error"),
+			)
+
 			fundReq.errChan <- err
 			return
 		}