It's often needed to check if an endpoint sits in the same DC as the
current node. It can be done by
topo.get_datacenter() == topo.get_datacenter(endpoint)
but in some cases a RAII filter function can be helpful.
Also there's a db::count_local_endpoints() that is surprisingly in use,
so add it to topology as well. Next patches will make use of both.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
ee0828b506