When direct failure detector was introduces the idea was that it will run on the same connection raft group0 verbs are running, but in60f1053087raft verbs were moved to run on the gossiper connection while DIRECT_FD_PING was left where it was. This patch move it to gossiper connection as well and fix the pinger code to run in gossiper scheduling group. (cherry picked from commit86dde50c0d)