lib/connections: Add KCP support (fixes #804)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3489

vendor/github.com/hashicorp/yamux/util.go

@@ -0,0 +1,28 @@
+package yamux
+
+// asyncSendErr is used to try an async send of an error
+func asyncSendErr(ch chan error, err error) {
+	if ch == nil {
+		return
+	}
+	select {
+	case ch <- err:
+	default:
+	}
+}
+
+// asyncNotify is used to signal a waiting goroutine
+func asyncNotify(ch chan struct{}) {
+	select {
+	case ch <- struct{}{}:
+	default:
+	}
+}
+
+// min computes the minimum of two values
+func min(a, b uint32) uint32 {
+	if a < b {
+		return a
+	}
+	return b
+}