adb: Set a hostname for mDNS

    start_mdns();

    std::lock_guard<std::mutex> lock(mdns_lock);

    auto error = DNSServiceRegister(&mdns_ref, 0, 0, nullptr, "_adb._tcp",

                                    nullptr, nullptr, htobe16((uint16_t)port),

                                    0, nullptr, mdns_callback, nullptr);

    std::string hostname = "adb-";

    hostname += android::base::GetProperty("ro.serialno", "unidentified");

    auto error = DNSServiceRegister(&mdns_ref, 0, 0, hostname.c_str(),

                                    kADBServiceType, nullptr, nullptr,

                                    htobe16((uint16_t)port), 0, nullptr,

                                    mdns_callback, nullptr);

    if (error != kDNSServiceErr_NoError) {

        LOG(ERROR) << "Could not register mDNS service (" << error << ").";