multi: update internals to support updating max htlc

In this commit, we update the router and link to support users
updating the max HTLC policy for their channels. By updating these internal
systems before updating the RPC server and lncli, we protect users from
being shown an option that doesn't actually work.

server.go

@@ -742,6 +742,7 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB,
 		ForAllOutgoingChannels:    s.chanRouter.ForAllOutgoingChannels,
 		PropagateChanPolicyUpdate: s.authGossiper.PropagateChanPolicyUpdate,
 		UpdateForwardingPolicies:  s.htlcSwitch.UpdateForwardingPolicies,
+		FetchChannel:              s.chanDB.FetchChannel,
 	}
 
 	utxnStore, err := newNurseryStore(activeNetParams.GenesisHash, chanDB)