multi: verify channel constraints on funding request

In this commit, the sanity checks in the CommitConstraints method is
moved out into a helper function called VerifyConstraints. This is done
so that the sanity checks can be performed more easily else where in the
code base. The new helper method is then called in the
handleInitFundingMsg method of the funding manager before the
OpenChannelMessage is sent.

funding/manager.go

@@ -4136,6 +4136,29 @@ func (f *Manager) handleInitFundingMsg(msg *InitFundingMsg) {
 	// remote party.
 	chanReserve := f.cfg.RequiredRemoteChanReserve(capacity, ourDustLimit)
 
+	// Check the sanity of the selected channel constraints.
+	channelConstraints := &channeldb.ChannelConstraints{
+		DustLimit:        ourDustLimit,
+		ChanReserve:      chanReserve,
+		MaxPendingAmount: maxValue,
+		MinHTLC:          minHtlcIn,
+		MaxAcceptedHtlcs: maxHtlcs,
+		CsvDelay:         remoteCsvDelay,
+	}
+	err = lnwallet.VerifyConstraints(
+		channelConstraints, resCtx.maxLocalCsv, capacity,
+	)
+	if err != nil {
+		_, reserveErr := f.cancelReservationCtx(peerKey, chanID, false)
+		if reserveErr != nil {
+			log.Errorf("unable to cancel reservation: %v",
+				reserveErr)
+		}
+
+		msg.Err <- err
+		return
+	}
+
 	// When opening a script enforced channel lease, include the required
 	// expiry TLV record in our proposal.
 	var leaseExpiry *lnwire.LeaseExpiry