Two main modifications:
  - source-specific routes are putted in front of the RIB,
  - route_stream now allows traversing all routes, all installed routes,
    or source-specific installed routes.

This fixes compilation under musl.

It also update the route's id.

Thanks to Julien Cristau.

This was requested by people who want to parse the local socket output
using sed/awk scripts.

Use the hostname instead of "alamakota" when announcing the router
on the local interface.  It would make it possible for visualisation
tools, such as babelweb, to display a meaningful name automatically.

FreeBSD system headers have their own "struct route", which made it
impossible to compile babeld. Switching babeld to "struct babel_route".

This changes the route table to be a sorted table of linked lists of
routes to a given prefix, which makes most route operations behave in
O(log n).  Insertion and flushing of a prefix is still O(n), but these
are fairly rare operations.

A nice side-effect is that the route table is now private to route.c,
which should make it easy to switch to a different data structure in
the future.

Run make EXTRA_DEFINES=-DNO_LOCAL_INTERFACE.