p2p: zero last seen timestamp when inserting a new peer

src/p2p/net_node.inl

@@ -1882,6 +1882,7 @@ namespace nodetool
         --i;
         continue;
       }
+      local_peerlist[i].last_seen = 0;
 
 #ifdef CRYPTONOTE_PRUNING_DEBUG_SPOOF_SEED
       be.pruning_seed = tools::make_pruning_seed(1 + (be.adr.as<epee::net_utils::ipv4_network_address>().ip()) % (1ul << CRYPTONOTE_PRUNING_LOG_STRIPES), CRYPTONOTE_PRUNING_LOG_STRIPES);