type safety for 'bool egress'

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I3f0a12f139478bc94d351d58a08d4a9bd19fa320
diff --git a/bpf_progs/bpf_net_helpers.h b/bpf_progs/bpf_net_helpers.h
index 1122f50..6bc3a67 100644
--- a/bpf_progs/bpf_net_helpers.h
+++ b/bpf_progs/bpf_net_helpers.h
@@ -87,9 +87,9 @@
     if (skb->data_end - skb->data < len) bpf_skb_pull_data(skb, len);
 }
 
-// constants for passing in to 'bool egress'
-static const bool INGRESS = false;
-static const bool EGRESS = true;
+struct egress_bool { bool egress; };
+#define INGRESS ((struct egress_bool){ .egress = false })
+#define EGRESS ((struct egress_bool){ .egress = true })
 
 // constants for passing in to 'bool downstream'
 static const bool UPSTREAM = false;