Improve firmware download status check.  Previous check was insufficient for
ATA since it ignored transport errors like command timeouts, while for SCSI
it was just wrong.
Fix and improve filemon(4) example:
- remove return statements from void function [1]
- include missing header
- use O_CLOEXEC instead of separate fcntl() calls

PR:		docs/179459 [1]
MFC after:	1 week