Use DirPort for uploading descriptors.

When we converted the horrible set of options that previously
controlled "use ORPort or DirPort? Anonymously or Non-anonymouly?" to
a single 'indirection' argument, we missed
directory_post_to_dirservers.

The problematic code was introduced in 5cbeb608, which went into
0.2.4.3-alpha.  This is a fix for bug 11469.