Fix the command to set NODE_IP

Change-Id: I345b5c887601d53e045e2d9aabc59ff8f4632e38
diff --git a/Makefile b/Makefile
index 0d82dee..63be427 100644
--- a/Makefile
+++ b/Makefile
@@ -36,7 +36,12 @@
 else
 	RAN_SUBNET := $(shell ip route | grep $${DATA_IFACE} | awk '/kernel/ {print $$1}')
 endif
-NODE_IP ?= $(shell ip route list default | awk -F 'src' '{ print $$2; exit }' | awk '{ print $$1 }')
+
+NODE_IP ?= $(shell ip route get 8.8.8.8 | grep -oP 'src \K\S+')
+ifndef NODE_IP
+$(error NODE_IP is not set)
+endif
+
 MME_IP  ?=
 
 HELM_GLOBAL_ARGS ?=