wgengine: log node IDs when peers are added/removed (#381)

Also stop logging data sent/received from nodes we're not connected to (ie all those `x`s being logged in the `peers: ` line)
Signed-off-by: Wendi <wendi.yu@yahoo.ca>

ipn/ipnserver/server_test.go

@@ -13,8 +13,6 @@ import (
 	"strings"
 	"testing"
 
-	"tailscale.com/types/logger"
-
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnserver"
 	"tailscale.com/safesocket"
@@ -34,14 +32,12 @@ func TestRunMultipleAccepts(t *testing.T) {
 	defer os.RemoveAll(td)
 	socketPath := filepath.Join(td, "tailscale.sock")
 
-	ulogf := func(format string, args ...interface{}) {
+	logf := func(format string, args ...interface{}) {
 		format = strings.TrimRight(format, "\n")
 		println(fmt.Sprintf(format, args...))
 		t.Logf(format, args...)
 	}
 
-	logf := logger.RateLimitedFn(ulogf, 1, 1, 100)
-
 	connect := func() {
 		for i := 1; i <= 2; i++ {
 			logf("connect %d ...", i)