Allow overriding ICE ufrag and pwd fields

Adds two new optional config keys - `iceUfrag` and `icePwd` which
are passed to libjuice.

Depends on: paullouisageneau/libjuice#249

Refs: paullouisageneau#1166

include/rtc/configuration.hpp

@@ -93,6 +93,10 @@ struct RTC_CPP_EXPORT Configuration {
 	optional<string> certificatePemFile;
 	optional<string> keyPemFile;
 	optional<string> keyPemPass;
+
+	// Overriding ICE ufrag/pwd
+	optional<string> iceUfrag;
+	optional<string> icePwd;
 };
 
 #ifdef RTC_ENABLE_WEBSOCKET

src/impl/icetransport.cpp

@@ -90,6 +90,14 @@ IceTransport::IceTransport(const Configuration &config, candidate_callback candi
 	jconfig.cb_recv = IceTransport::RecvCallback;
 	jconfig.user_ptr = this;
 
+	if (config.iceUfrag) {
+		jconfig.ice_ufrag = config.iceUfrag->c_str();
+	}
+
+	if (config.icePwd) {
+		jconfig.ice_pwd = config.icePwd->c_str();
+	}
+
 	if (config.enableIceTcp) {
 		PLOG_WARNING << "ICE-TCP is not supported with libjuice";
 	}