Fixes the binding error when SMP in tandem with a Unix domain socket

lib/roles/http/server/server.c

@@ -131,6 +131,17 @@ done_list:
 
 	(void)n;
 #if defined(__linux__)
+#ifdef LWS_WITH_UNIX_SOCK
+	/*
+	 * A Unix domain sockets cannot be bound for several times, even if we set
+	 * the SO_REUSE* options on.
+	 * However, fortunately, each thread is able to independently listen when
+	 * running on a reasonably new Linux kernel. So we can safely assume
+	 * creating just one listening socket for a multi-threaded environment won't
+	 * fail in most cases.
+	 */
+	if (!LWS_UNIX_SOCK_ENABLED(vhost))
+#endif
 	limit = vhost->context->count_threads;
 #endif