server: add --exit-no-conn option (#1029)

Co-authored-by: Shuanglei Tao <tsl0922@gmail.com>

src/server.h

@@ -59,7 +59,7 @@ struct pss_tty {
 typedef struct {
   struct pss_tty *pss;
   bool ws_closed;
-} pty_ctx_t ;
+} pty_ctx_t;
 
 struct server {
   int client_count;        // client count
@@ -78,6 +78,7 @@ struct server {
   bool check_origin;       // whether allow websocket connection from different origin
   int max_clients;         // maximum clients to support
   bool once;               // whether accept only one client and exit on disconnection
+  bool exit_no_conn;       // whether exit on all clients disconnection
   char socket_path[255];   // UNIX domain socket path
   char terminal_type[30];  // terminal type to report