Validate the mode argument in access, eaccess, and faccessat for optional
POSIX compliance and to improve compatibility with Linux and NetBSD

The issue was identified with lib/libc/sys/t_access:access_inval from
NetBSD

Update the manpage accordingly

PR: 181155
Reviewed by: jilles (code), jmmv (code), wblock (manpage), wollman (code)
MFC after: 4 weeks
Phabric: D678 (code), D786 (manpage)
Sponsored by: EMC / Isilon Storage Division
Bump .Dd for the content change done in r271639

PR: 181155
Sponsored by: EMC / Isilon Storage Division