Add m_inbound_onion to AttemptToEvictConnection()

and an `m_is_onion` struct member to NodeEvictionCandidate and tests.

We'll use these in the peer eviction logic to protect inbound onion peers
in addition to the existing protection of localhost peers.

src/net.cpp

@@ -992,7 +992,8 @@ bool CConnman::AttemptToEvictConnection()
                                                node->nLastBlockTime, node->nLastTXTime,
                                                HasAllDesirableServiceFlags(node->nServices),
                                                peer_relay_txes, peer_filter_not_null, node->nKeyedNetGroup,
-                                               node->m_prefer_evict, node->addr.IsLocal()};
+                                               node->m_prefer_evict, node->addr.IsLocal(),
+                                               node->m_inbound_onion};
             vEvictionCandidates.push_back(candidate);
         }
     }