htlcswitch+channel: add channel states synchronization

In this commit BOLT№2 retranmission logic for the channel link have
been added. Now if channel link have been initialised with the
'SyncState' field than it will send the lnwire.ChannelReestablish
message and will be waiting for receiving the same message from remote
side. Exchange of this message allow both sides understand which
updates they should exchange with each other in order sync their
states.

peer.go

@@ -399,6 +399,7 @@ func (p *peer) loadActiveChannels(chans []*channeldb.OpenChannel) error {
 			Switch:           p.server.htlcSwitch,
 			FwrdingPolicy:    *forwardingPolicy,
 			BlockEpochs:      blockEpoch,
+			SyncStates:       true,
 		}
 		link := htlcswitch.NewChannelLink(linkCfg, lnChan,
 			uint32(currentHeight))
@@ -745,6 +746,9 @@ out:
 		case *lnwire.UpdateFee:
 			isChanUpdate = true
 			targetChan = msg.ChanID
+		case *lnwire.ChannelReestablish:
+			isChanUpdate = true
+			targetChan = msg.ChanID
 
 		case *lnwire.ChannelUpdate,
 			*lnwire.ChannelAnnouncement,
@@ -1261,6 +1265,7 @@ out:
 				Switch:           p.server.htlcSwitch,
 				FwrdingPolicy:    p.server.cc.routingPolicy,
 				BlockEpochs:      blockEpoch,
+				SyncStates:       false,
 			}
 			link := htlcswitch.NewChannelLink(linkConfig, newChan,
 				uint32(currentHeight))