Extend the '--capture' option with and optional numerical argument to be able to specify how many frames to capture before exiting. If the optional argument is not provided the old behavior of running until the user interrupts with a SIGINT is retained. Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>