Return simple responses immediatly

This commit rearranges the poll handler to immediatly accept
updates and notify its peers and return, not travel down the
function for a bit. This reduces the DB calls and other
holdups that isnt necessary to send a "lite response", a
map response without peers, or accepting an endpoint update.

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/app.go

@@ -94,8 +94,6 @@ type Headscale struct {
 
 	shutdownChan       chan struct{}
 	pollNetMapStreamWG sync.WaitGroup
-
-	pollStreamOpenMu sync.Mutex
 }
 
 func NewHeadscale(cfg *types.Config) (*Headscale, error) {