### 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
: addrman(addrman_in), nSeed0(nSeed0In), nSeed1(nSeed1In)
{
    SetTryNewOutboundPeer(false);
    Options connOptions;
    Init(connOptions);
    SetNetworkActive(network_active);
}
NodeId CConnman::GetNewNodeId()
{
    return nLastNodeId.fetch_add(1, std::memory_order_relaxed);
}
bool CConnman::Bind(const CService &addr, unsigned int flags, NetPermissionFlags permissions) {
    if (!(flags & BF_EXPLICIT) && !IsReachable(addr))
        return false;
    bilingual_str strError;
    if (!BindListenPort(addr, strError, permissions)) {
        if ((flags & BF_REPORT_ERROR) && clientInterface) {
            clientInterface->ThreadSafeMessageBox(strError, "", CClientUIInterface::MSG_ERROR);
        }
        return false;
    }
    if (addr.IsRoutable() && fDiscover && !(flags & BF_DONT_ADVERTISE) && !(permissions & PF_NOBAN)) {
        AddLocal(addr, LOCAL_BIND);
    }
    return true;
}
bool CConnman::InitBinds(