lnwallet+funding: pass the pending channel ID into the reservation context

In this commit, we start to thread the pending channel ID from wire
protocol all the way down into the reservation context. This change will
allow negotiation to take place _outside_ the protocol that may result
in a particular chanfunding.Assembler being dispatched.

fundingmanager.go

@@ -1216,6 +1216,7 @@ func (f *fundingManager) handleFundingOpen(fmsg *fundingOpenMsg) {
 	chainHash := chainhash.Hash(msg.ChainHash)
 	req := &lnwallet.InitFundingReserveMsg{
 		ChainHash:        &chainHash,
+		PendingChanID:    msg.PendingChannelID,
 		NodeID:           fmsg.peer.IdentityKey(),
 		NodeAddr:         fmsg.peer.Address(),
 		LocalFundingAmt:  0,
@@ -2781,6 +2782,10 @@ func (f *fundingManager) handleInitFundingMsg(msg *initFundingMsg) {
 		channelFlags = lnwire.FFAnnounceChannel
 	}
 
+	// Obtain a new pending channel ID which is used to track this
+	// reservation throughout its lifetime.
+	chanID := f.nextPendingChanID()
+
 	// Initialize a funding reservation with the local wallet. If the
 	// wallet doesn't have enough funds to commit to this channel, then the
 	// request will fail, and be aborted.
@@ -2798,6 +2803,7 @@ func (f *fundingManager) handleInitFundingMsg(msg *initFundingMsg) {
 	tweaklessCommitment := localTweakless && remoteTweakless
 	req := &lnwallet.InitFundingReserveMsg{
 		ChainHash:        &msg.chainHash,
+		PendingChanID:    chanID,
 		NodeID:           peerKey,
 		NodeAddr:         msg.peer.Address(),
 		SubtractFees:     msg.subtractFees,
@@ -2823,11 +2829,7 @@ func (f *fundingManager) handleInitFundingMsg(msg *initFundingMsg) {
 	// SubtractFees=true.
 	capacity := reservation.Capacity()
 
-	// Obtain a new pending channel ID which is used to track this
-	// reservation throughout its lifetime.
-	chanID := f.nextPendingChanID()
-
-	fndgLog.Infof("Target commit tx sat/kw for pending_id(%x): %v", chanID,
+	fndgLog.Infof("Target commit tx sat/kw for pendingID(%x): %v", chanID,
 		int64(commitFeePerKw))
 
 	// If the remote CSV delay was not set in the open channel request,