channeldb: add BalanceAboveReserve helper

We add this helper which will be used in a following commit. For the
noop htlcs that we are going to add we need to know whether the
"potential" receiver's balance is above reserve, so we add this
specific helper that helps us safely perform this check.

Author: GeorgeTsagk

channeldb/channel.go

@@ -2127,6 +2127,28 @@ func (c *OpenChannel) clearChanStatus(status ChannelStatus) error {
 	return nil
 }
 
+// BalanceAboveReserve checks if the balance for the provided party is above the
+// configured reserve.
+func (c *OpenChannel) BalanceAboveReserve(
+	party lntypes.ChannelParty) bool {
+
+	c.Lock()
+	defer c.Unlock()
+
+	switch {
+	case party.IsLocal():
+		return c.LocalCommitment.LocalBalance.ToSatoshis() >
+			c.LocalChanCfg.ChanReserve
+
+	case party.IsRemote():
+		return c.RemoteCommitment.RemoteBalance.ToSatoshis() >
+			c.RemoteChanCfg.ChanReserve
+
+	}
+
+	return false
+}
+
 // putOpenChannel serializes, and stores the current state of the channel in its
 // entirety.
 func putOpenChannel(chanBucket kvdb.RwBucket, channel *OpenChannel) error {