MFC r334403:

#include <bsm/audit.h> in security/audit/audit_ioctl.h

security/audit/audit_ioctl.h uses a type from bsm/audit.h, so needs to
include it. And it needs to know the type's size, so it can't just
forward-declare.

PR: 228470
Submitted by: aniketp
Sponsored by: Google, Inc. (GSoC 2018)
Differential Revision: https://reviews.freebsd.org/D15561