ring: use turn.ring.cx as default TURN server

Give a default TURN server at Ring account creation.
This server is a proposed by Savoir-faire Linux.

Change-Id: I95b4c8d3e9a7efe0fcd109a5ba7246927723dced

src/ringdht/ringaccount.cpp

@@ -79,6 +79,10 @@ static constexpr auto ICE_NEGOTIATION_TIMEOUT = std::chrono::seconds(60);
 static constexpr auto TLS_TIMEOUT = std::chrono::seconds(30);
 
 static constexpr const char * const RING_URI_PREFIX = "ring:";
+static constexpr const char * DEFAULT_TURN_SERVER = "turn.ring.cx";
+static constexpr const char * DEFAULT_TURN_USERNAME = "ring";
+static constexpr const char * DEFAULT_TURN_PWD = "ring";
+static constexpr const char * DEFAULT_TURN_REALM = "ring";
 
 constexpr const char * const RingAccount::ACCOUNT_TYPE;
 /* constexpr */ const std::pair<uint16_t, uint16_t> RingAccount::DHT_PORT_RANGE {4000, 8888};
@@ -142,6 +146,13 @@ RingAccount::RingAccount(const std::string& accountID, bool /* presenceEnabled *
     cachePath_ = fileutils::get_cache_dir()+DIR_SEPARATOR_STR+getAccountID();
     dataPath_ = cachePath_ + DIR_SEPARATOR_STR "values";
     idPath_ = fileutils::get_data_dir()+DIR_SEPARATOR_STR+getAccountID();
+
+    // Force the SFL turn server if none provided yet
+    turnServer_ = DEFAULT_TURN_SERVER;
+    turnServerUserName_ = DEFAULT_TURN_USERNAME;
+    turnServerPwd_ = DEFAULT_TURN_PWD;
+    turnServerRealm_ = DEFAULT_TURN_REALM;
+    turnEnabled_ = true;
 }
 
 RingAccount::~RingAccount()
@@ -525,6 +536,7 @@ void
 RingAccount::setAccountDetails(const std::map<std::string, std::string> &details)
 {
     SIPAccountBase::setAccountDetails(details);
+
     if (hostname_.empty())
         hostname_ = DHT_DEFAULT_BOOTSTRAP;
     parseInt(details, Conf::CONFIG_DHT_PORT, dhtPort_);