### 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
s.clear();
    BOOST_REQUIRE(addr.SetSpecial("kpgvmscirrdqpekbqjsvw5teanhatztpp2gl6eee4zkowvwfxwenqaid.onion"));
    s << addr;
    BOOST_CHECK_EQUAL(HexStr(s), "042053cd5648488c4707914182655b7664034e09e66f7e8cbf1084e654eb56c5bd88");
    s.clear();
    BOOST_REQUIRE(addr.SetInternal("a"));
    s << addr;
    BOOST_CHECK_EQUAL(HexStr(s), "0210fd6b88c08724ca978112ca1bbdcafac2");
    s.clear();
}
BOOST_AUTO_TEST_CASE(cnetaddr_unserialize_v2)
{
    CNetAddr addr;
    CDataStream s(SER_NETWORK, PROTOCOL_VERSION);
    
    
    s.SetVersion(s.GetVersion() | ADDRV2_FORMAT);
    
    s << MakeSpan(ParseHex("01"          
                           "04"          
                           "01020304")); 
    s >> addr;
    BOOST_CHECK(addr.IsValid());
    BOOST_CHECK(addr.IsIPv4());
    BOOST_CHECK(addr.IsAddrV1Compatible());
    BOOST_CHECK_EQUAL(addr.ToString(), "1.2.3.4");
    BOOST_REQUIRE(s.empty());
    
    s << MakeSpan(ParseHex("01"      
                           "04"