### FEATURE REQUEST

Currently, when a bitcoin node is set up with a connection to both TOR and normal IPv4/6 internet, the 8 outbound-only connection slots, almost always get filled with nodes connecting over IP.
Adding a config option, which would try to ballance these connections based on what kind of network they go through, would be benefficial in many ways:

1. It would add edges between bitcoin network on TOR and normal internet, reducing delays, and the risks associated with an attacker isolating a part of TOR-bitcoin-network from the rest of the world
(Or an ISP/government man-in-the-middling all the normal IP connections)

2. It would help hide/annonymise normal user's transactions from his/her ISP, by mixing them with TOR-outbound ones

3. It would reduce the stress on normal general purpose TOR exit nodes, as users would more likely/reliably connect to TOR-IPv4/6 bitcoin nodes instead of exiting into normal internet first, and then connecting to default IPv4/6-only bitcoin nodes

I understand it is possible to create such bridges already, by forcing connections to TOR-only nodes, or by just running a node with lots of inbound slots, but I think the proposed option, would greatly increase the number of such relays, and remove the need for user to maintain a TOR-node whitelist, by handing this work off to normal bitcoind connection finding algorithm.

This could be implemented as a minimum number of connections for each network, or just a simple evening boolean switch. (Which could be enabled by default for bitcoind installs with TOR connectivity)

In the future, if bitcoin was to support a new network type (for example cjdns/I2P/GNUnet), this option would help establish a presence on the new network faster

bitcoind: 0.15
if (nInbound >= nMaxInbound)
    {
        if (!AttemptToEvictConnection()) {
            
            LogPrint(BCLog::NET, "failed to find an eviction candidate - connection dropped (full)\n");
            CloseSocket(hSocket);
            return;
        }
    }
    NodeId id = GetNewNodeId();
    uint64_t nonce = GetDeterministicRandomizer(RANDOMIZER_ID_LOCALHOSTNONCE).Write(id).Finalize();
    ServiceFlags nodeServices = nLocalServices;
    if (NetPermissions::HasFlag(permissionFlags, PF_BLOOMFILTER)) {
        nodeServices = static_cast<ServiceFlags>(nodeServices | NODE_BLOOM);
    }
    const bool inbound_onion = std::find(m_onion_binds.begin(), m_onion_binds.end(), addr_bind) != m_onion_binds.end();
    CNode* pnode = new CNode(id, nodeServices, hSocket, addr, CalculateKeyedNetGroup(addr), nonce, addr_bind, "", ConnectionType::INBOUND, inbound_onion);
    pnode->AddRef();
    pnode->m_permissionFlags = permissionFlags;
    pnode->m_prefer_evict = discouraged;
    m_msgproc->InitializeNode(pnode);
    LogPrint(BCLog::NET, "connection from %s accepted\n", addr.ToString());
    {
        LOCK(cs_vNodes);
        vNodes.push_back(pnode);
    }
    
    RandAddEvent((uint32_t)id);
}
bool CConnman::AddConnection(const std::string& address, ConnectionType conn_type)