[VOL-1503] Add a GetMembership API to the core

This API is used by the Affinity Router to query the Go Core
for its membership info, it any.

Change-Id: I46aac8579a0452b665175cbd379876a702cce102
diff --git a/common/core/northbound/grpc/default_api_handler.go b/common/core/northbound/grpc/default_api_handler.go
index 30320a2..b6cd185 100644
--- a/common/core/northbound/grpc/default_api_handler.go
+++ b/common/core/northbound/grpc/default_api_handler.go
@@ -42,6 +42,11 @@
 	return nil, errors.New("UnImplemented")
 }
 
+func (handler *DefaultAPIHandler) GetMembership(ctx context.Context, empty *empty.Empty) (*voltha.Membership, error) {
+	log.Debug("GetMembership-request")
+	return nil, errors.New("UnImplemented")
+}
+
 func (handler *DefaultAPIHandler) UpdateMembership(ctx context.Context, membership *voltha.Membership) (*empty.Empty, error) {
 	log.Debugw("UpdateMembership-request", log.Fields{"membership": membership})
 	return nil, errors.New("UnImplemented")