Fix peer tags configuration (#3132)

Co-authored-by: Dario Castañé <[email protected]>

Author: ichinaski

ddtrace/tracer/option.go

@@ -774,6 +774,7 @@ func loadAgentFeatures(agentDisabled bool, agentURL *url.URL, httpClient *http.C
 	features.DropP0s = info.ClientDropP0s
 	features.StatsdPort = info.Config.StatsdPort
 	features.metaStructAvailable = info.SpanMetaStruct
+	features.peerTags = info.PeerTags
 	for _, endpoint := range info.Endpoints {
 		switch endpoint {
 		case "/v0.6/stats":

ddtrace/tracer/option_test.go

@@ -224,7 +224,7 @@ func TestLoadAgentFeatures(t *testing.T) {
 
 	t.Run("OK", func(t *testing.T) {
 		srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
-			w.Write([]byte(`{"endpoints":["/v0.6/stats"],"feature_flags":["a","b"],"client_drop_p0s":true,"config": {"statsd_port":8999}}`))
+			w.Write([]byte(`{"endpoints":["/v0.6/stats"],"feature_flags":["a","b"],"client_drop_p0s":true,"peer_tags":["peer.hostname"],"config": {"statsd_port":8999}}`))
 		}))
 		defer srv.Close()
 		cfg := newConfig(WithAgentAddr(strings.TrimPrefix(srv.URL, "http://")), WithAgentTimeout(2))
@@ -237,6 +237,7 @@ func TestLoadAgentFeatures(t *testing.T) {
 		assert.True(t, cfg.agent.Stats)
 		assert.True(t, cfg.agent.HasFlag("a"))
 		assert.True(t, cfg.agent.HasFlag("b"))
+		assert.EqualValues(t, cfg.agent.peerTags, []string{"peer.hostname"})
 	})
 
 	t.Run("discovery", func(t *testing.T) {