api: serve the websocket with wslay instead of headsocket (#887)

`HeadSocket` library we are currently using is full of bugs and no
longer maintained. Swap it out with `wslay`.

src/spice2x/external/wslay/wslay_net.c

@@ -0,0 +1,35 @@
+/*
+ * Wslay - The WebSocket Library
+ *
+ * Copyright (c) 2011, 2012 Tatsuhiro Tsujikawa
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+#include "wslay_net.h"
+
+#ifndef WORDS_BIGENDIAN
+
+uint64_t wslay_byteswap64(uint64_t x) {
+  uint64_t u = ntohl(x & 0xffffffffllu);
+  uint64_t l = ntohl((uint32_t)(x >> 32));
+  return (u << 32) | l;
+}
+
+#endif /* !WORDS_BIGENDIAN */