bgpd: route suppression refactory

bgpd: route suppression refactory

Instead of just counting the route suppressions, keep a reference for
all aggregations that are doing it. It should help the with the
following problems:

- Which aggregation suppressed the route.
- Double suppression
- Double unsuppression
- Avoids calling `bgp_process` if already suppressed/unsuppressed.
- Easier code maintenance and understanding

This also fixes a crash when modifying a route map that is
associated with a working aggregate-address.

Signed-off-by: Rafael Zalamena <rzalamena@opensourcerouting.org>