Fixes for building on v4.0

Signed-off-by: Mike Marchetti <mmarchetti@sandvine.com>
Change-Id: I3f24280ee0cc745a512e8879990f2dfa86d0feda
diff --git a/Makefile b/Makefile
index 8e0da21..7548100 100644
--- a/Makefile
+++ b/Makefile
@@ -61,6 +61,7 @@
 
 osm-im:
 	$(shell git clone https://osm.etsi.org/gerrit/osm/IM)
+	git -C IM checkout $(BRANCH)
 	make -C IM clean all
 
 package: prepare