fix: linux, weak network, repeated keys (#10211)

Use `press` as the `click` flag on Linux to avoid repeated keys, like
the Legacy mode.

Signed-off-by: fufesou <linlong1266@gmail.com>

libs/hbb_common/protos/message.proto

@@ -284,7 +284,9 @@ enum ControlKey {
 }
 
 message KeyEvent {
+  // `down` indicates the key's state(down or up).
   bool down = 1;
+  // `press` indicates a click event(down and up).
   bool press = 2;
   oneof union {
     ControlKey control_key = 3;