Make the proxy to report the number of clients to the broker

So the assignment of proxies is based on the load. The number of clients
is ronded down to 8. Existing proxies that doesn't report the number
of clients will be distributed equaly to new proxies until they get 8
clients, that is okish as the existing proxies do have a maximum
capacity of 10.

Fixes #40048

proxy/tokens.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"sync/atomic"
+)
+
+type tokens_t struct {
+	ch       chan struct{}
+	capacity uint
+	clients  int64
+}
+
+func newTokens(capacity uint) *tokens_t {
+	var ch chan struct{}
+	if capacity != 0 {
+		ch = make(chan struct{}, capacity)
+	}
+
+	return &tokens_t{
+		ch:       ch,
+		capacity: capacity,
+		clients:  0,
+	}
+}
+
+func (t *tokens_t) get() {
+	atomic.AddInt64(&t.clients, 1)
+
+	if t.capacity != 0 {
+		t.ch <- struct{}{}
+	}
+}
+
+func (t *tokens_t) ret() {
+	atomic.AddInt64(&t.clients, -1)
+
+	if t.capacity != 0 {
+		<-t.ch
+	}
+}
+
+func (t tokens_t) count() int64 {
+	return atomic.LoadInt64(&t.clients)
+}