Allow custom routes inside UPF

This is required to work around liveness failure in a single interface
machine where Kubelet node IP is part of eNB subnet.

Change-Id: I37549d89fbe7e045e6639295c29652ba0d6fb5e4
diff --git a/bess-upf/values.yaml b/bess-upf/values.yaml
index e48d0b3..bf1a8e0 100644
--- a/bess-upf/values.yaml
+++ b/bess-upf/values.yaml
@@ -65,6 +65,10 @@
       enabled: true
     # Dynamic IP allocation is not supported yet
     ipam: static
+    # Custom routes inside UPF
+    #routes:
+    #  - to: 10.76.28.173/32
+    #    via: 169.254.1.1
     cniPlugin: vfioveth
     enb:
       subnet: 192.168.251.0/24