reformat code (#2019)

* reformat code

This is mostly an automated change with `make lint`.
I had to manually please golangci-lint in routes_test because of a short
variable name.

* fix start -> strategy which was wrongly corrected by linter

hscontrol/mapper/mapper.go

@@ -541,7 +541,6 @@ func appendPeerChanges(
 	changed types.Nodes,
 	cfg *types.Config,
 ) error {
-
 	packetFilter, err := pol.CompileFilterRules(append(peers, node))
 	if err != nil {
 		return err