Update manual page references and macros to align to mandoc syntax

Update manual page references and macros to align to mandoc syntax

xlocale.3: Comment out reference to atof_l(3), atoi_l(3), atol_l(3), atoll_l(3)
  These manual page references do not exist.

lagg.4: Change the reference for /etc/rc.conf from a reference link
  .Xr -> .Pa based on the context within the manual page it is used.

buf.9: Remove .Xr entries from the file
  The buf.9 manual page contains a commented out .Xr reference.
  The <filmmein> 9 entry is a placeholder and has been removed for
  clarity.

Reviewed by:	mhorne
Pull Request:	https://github.com/freebsd/freebsd-src/pull/1114