Remove authenticate section.

You should be using the PAP module, which does all of this.
Remove extraneous tab
Convert pairmake() to talloc

And add a VALUE_PAIR**vps to it.  If vps != NULL, the newly
created VP is added to the list.

This API change cleans up the code rather substantially
Move recv() functions to talloc.

They still use a NULL context for rad_alloc(), but that
can be fixed in another stage