It's not clear to me if dropping support for this functionality was intentional.

Chain of events:

- #21689 removed test coverage due to a misunderstanding due, I believe, to this functionality being generally supported by all platforms except macOS which does not and returns a different format
- #21756 removed support and caused this regression
- #21690 restores the test coverage that would have caught this regression

Currently, neither the test coverage before #21689 nor the coverage restored by #21690 pass since the merge of #21756.

REACH_UNREACHABLE,
        REACH_DEFAULT,
        REACH_TEREDO,
        REACH_IPV6_WEAK,
        REACH_IPV4,
        REACH_IPV6_STRONG,
        REACH_PRIVATE
    };
    if (!IsRoutable() || IsInternal())
        return REACH_UNREACHABLE;
    int ourNet = GetExtNetwork(this);
    int theirNet = GetExtNetwork(paddrPartner);
    bool fTunnel = IsRFC3964() || IsRFC6052() || IsRFC6145();
    switch(theirNet) {
    case NET_IPV4:
        switch(ourNet) {
        default:       return REACH_DEFAULT;
        case NET_IPV4: return REACH_IPV4;
        }
    case NET_IPV6:
        switch(ourNet) {
        default:         return REACH_DEFAULT;
        case NET_TEREDO: return REACH_TEREDO;
        case NET_IPV4:   return REACH_IPV4;
        case NET_IPV6:   return fTunnel ? REACH_IPV6_WEAK : REACH_IPV6_STRONG; 
        }
    case NET_ONION:
        switch(ourNet) {
        default:         return REACH_DEFAULT;
        case NET_IPV4:   return REACH_IPV4;