### 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
BF_NONE         = 0,
    BF_EXPLICIT     = (1U << 0),
    BF_REPORT_ERROR = (1U << 1),
    /**
     * Do not call AddLocal() for our special addresses, e.g., for incoming
     * Tor connections, to prevent gossiping them over the network.
     */
    BF_DONT_ADVERTISE = (1U << 2),
};
static const uint64_t SELECT_TIMEOUT_MILLISECONDS = 50;
const std::string NET_MESSAGE_COMMAND_OTHER = "*other*";
static const uint64_t RANDOMIZER_ID_NETGROUP = 0x6c0edd8036ef4036ULL; 
static const uint64_t RANDOMIZER_ID_LOCALHOSTNONCE = 0xd93e69e2bbfa5735ULL; 
static const uint64_t RANDOMIZER_ID_ADDRCACHE = 0x1cf2e4ddd306dda9ULL; 
bool fDiscover = true;
bool fListen = true;
RecursiveMutex cs_mapLocalHost;
std::map<CNetAddr, LocalServiceInfo> mapLocalHost GUARDED_BY(cs_mapLocalHost);
static bool vfLimited[NET_MAX] GUARDED_BY(cs_mapLocalHost) = {};
std::string strSubVersion;
void CConnman::AddAddrFetch(const std::string& strDest)
{
    LOCK(m_addr_fetches_mutex);
    m_addr_fetches.push_back(strDest);
}
uint16_t GetListenPort()