routing+discovery: extract local channel manager

The policy update logic that resided part in the gossiper and
part in the rpc server is extracted into its own object.

This prepares for additional validation logic to be added for policy
updates that would otherwise make the gossiper heavier.

It is also a small first step towards separation of our own channel data
from the rest of the graph.

rpcserver.go

@@ -4545,12 +4545,6 @@ func (r *rpcServer) FeeReport(ctx context.Context,
 // 0.000001, or 0.0001%.
 const minFeeRate = 1e-6
 
-// policyUpdateLock ensures that the database and the link do not fall out of
-// sync if there are concurrent fee update calls. Without it, there is a chance
-// that policy A updates the database, then policy B updates the database, then
-// policy B updates the link, then policy A updates the link.
-var policyUpdateLock sync.Mutex
-
 // UpdateChannelPolicy allows the caller to update the channel forwarding policy
 // for all channels globally, or a particular channel.
 func (r *rpcServer) UpdateChannelPolicy(ctx context.Context,
@@ -4615,22 +4609,13 @@ func (r *rpcServer) UpdateChannelPolicy(ctx context.Context,
 		req.BaseFeeMsat, req.FeeRate, feeRateFixed, req.TimeLockDelta,
 		spew.Sdump(targetChans))
 
-	// With the scope resolved, we'll now send this to the
-	// AuthenticatedGossiper so it can propagate the new policy for our
-	// target channel(s).
-	policyUpdateLock.Lock()
-	defer policyUpdateLock.Unlock()
-	chanPolicies, err := r.server.authGossiper.PropagateChanPolicyUpdate(
-		chanPolicy, targetChans...,
-	)
+	// With the scope resolved, we'll now send this to the local channel
+	// manager so it can propagate the new policy for our target channel(s).
+	err := r.server.localChanMgr.UpdatePolicy(chanPolicy, targetChans...)
 	if err != nil {
 		return nil, err
 	}
 
-	// Finally, we'll apply the set of channel policies to the target
-	// channels' links.
-	r.server.htlcSwitch.UpdateForwardingPolicies(chanPolicies)
-
 	return &lnrpc.PolicyUpdateResponse{}, nil
 }