Gauge add

Change-Id: I6e1fdec0741f9e0bbbf5c330a8d146095afc6a44
Signed-off-by: Juha Hyttinen <juha.hyttinen@nokia.com>
diff --git a/pkg/xapp/metrics.go b/pkg/xapp/metrics.go
index f85c488..40adbcd 100644
--- a/pkg/xapp/metrics.go
+++ b/pkg/xapp/metrics.go
@@ -89,6 +89,12 @@
 	met.gauges[metric].Set(val)
 }
 
+func (met *MetricGroupsCache) GAdd(metric string, val float64) {
+	met.RLock()
+	defer met.RUnlock()
+	met.gauges[metric].Add(val)
+}
+
 func (met *MetricGroupsCache) GInc(metric string) {
 	met.RLock()
 	defer met.RUnlock()