server.go+accessman.go: introduce caches for access permissions

Here we introduce the access manager which has caches that will
determine the access control status of our peers. Peers that have
had their funding transaction confirm with us are protected. Peers
that only have pending-open channels with us are temporary access
and can have their access revoked. The rest of the peers are granted
restricted access.

discovery/syncer.go

@@ -181,6 +181,9 @@ const (
 	// requestBatchSize is the maximum number of channels we will query the
 	// remote peer for in a QueryShortChanIDs message.
 	requestBatchSize = 500
+
+	// syncerBufferSize is the size of the syncer's buffers.
+	syncerBufferSize = 5
 )
 
 var (
@@ -436,8 +439,8 @@ func newGossipSyncer(cfg gossipSyncerCfg, sema chan struct{}) *GossipSyncer {
 		rateLimiter:        rateLimiter,
 		syncTransitionReqs: make(chan *syncTransitionReq),
 		historicalSyncReqs: make(chan *historicalSyncReq),
-		gossipMsgs:         make(chan lnwire.Message, 100),
-		queryMsgs:          make(chan lnwire.Message, 100),
+		gossipMsgs:         make(chan lnwire.Message, syncerBufferSize),
+		queryMsgs:          make(chan lnwire.Message, syncerBufferSize),
 		syncerSema:         sema,
 		quit:               make(chan struct{}),
 	}