### 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
pollfds[socket_id].fd = socket_id;
        pollfds[socket_id].events |= POLLIN;
    }
    for (SOCKET socket_id : send_select_set) {
        pollfds[socket_id].fd = socket_id;
        pollfds[socket_id].events |= POLLOUT;
    }
    for (SOCKET socket_id : error_select_set) {
        pollfds[socket_id].fd = socket_id;
        
        pollfds[socket_id].events |= POLLERR|POLLHUP;
    }
    std::vector<struct pollfd> vpollfds;
    vpollfds.reserve(pollfds.size());
    for (auto it : pollfds) {
        vpollfds.push_back(std::move(it.second));
    }
    if (poll(vpollfds.data(), vpollfds.size(), SELECT_TIMEOUT_MILLISECONDS) < 0) return;
    if (interruptNet) return;
    for (struct pollfd pollfd_entry : vpollfds) {
        if (pollfd_entry.revents & POLLIN)            recv_set.insert(pollfd_entry.fd);
        if (pollfd_entry.revents & POLLOUT)           send_set.insert(pollfd_entry.fd);
        if (pollfd_entry.revents & (POLLERR|POLLHUP)) error_set.insert(pollfd_entry.fd);
    }
}
#else
void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_set, std::set<SOCKET> &error_set)
{
    std::set<SOCKET> recv_select_set, send_select_set, error_select_set;
    if (!GenerateSelectSet(recv_select_set, send_select_set, error_select_set)) {