Fields
- msgh_trailer_type: mach_msg_trailer_type_t
- msgh_trailer_size: mach_msg_trailer_size_t
- msgh_seqno: mach_port_seqno_t
- msgh_sender: security_token_t
- msgh_audit: audit_token_t
- msgh_context: mach_port_context_t
- msgh_ad: s32
- msgh_labels: msg_labels_t