Since it's a route attribute, it fits better there.

Add 3 new options to configuration and manpages:
src-ip, src-eq, src-le and src-ge.

It also update the route's id.

The field "result" is in fact an additional cost.

This is a MUST according to the Babel Extension Mechanism draft
(Section 2.2.3).

This reverts commit bf8555b2.