pam.d: install hard link with same mode as target
Previously when using NO_ROOT we recorded a METALOG entry for the
pam.d/ftp hard link with a different file mode than the link target
pam.d/ftpd, which is not permitted.
This change is similar to 1dbb9994d4dd for .profile
Sponsored by: The FreeBSD Foundation
(cherry picked from commit f2865d7d550161bf4058425a6677a839c065bde4)