Do not set SECCOMP_FILTER_FLAG_NEW_LISTENER as seccomp attribute.
Prior to libseccomp merging support for SECCOMP_RET_USER_NOTIF there was a
libseccomp specific attribute that needed to be set before
SECCOMP_RET_USER_NOTIF could be used. This has been removed.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>