ipn, control/controlclient: fix some data races

More remain.

Fixes tailscale/corp#432

control/controlclient/direct.go

@@ -456,7 +456,7 @@ func (c *Direct) PollNetMap(ctx context.Context, maxPolls int, cb func(*NetworkM
 	persist := c.persist
 	serverURL := c.serverURL
 	serverKey := c.serverKey
-	hostinfo := c.hostinfo
+	hostinfo := c.hostinfo.Clone()
 	backendLogID := hostinfo.BackendLogID
 	localPort := c.localPort
 	ep := append([]string(nil), c.endpoints...)

ipn/local.go

@@ -712,11 +712,12 @@ func (b *LocalBackend) SetPrefs(new *Prefs) {
 		newHi.Hostname = h
 	}
 	b.hostinfo = newHi
+	hostInfoChanged := !oldHi.Equal(newHi)
 	b.mu.Unlock()
 
 	b.logf("SetPrefs: %v", new.Pretty())
 
-	if old.ShieldsUp != new.ShieldsUp || !oldHi.Equal(newHi) {
+	if old.ShieldsUp != new.ShieldsUp || hostInfoChanged {
 		b.doSetHostinfoFilterServices(newHi)
 	}