cosmetic: use macro for gtphub plane iteration

Change-Id: If82fcd9f6509da60e6f0d916fe107de1b38bfd18
diff --git a/src/gprs/gtphub.c b/src/gprs/gtphub.c
index 5e962f2..76eebb1 100644
--- a/src/gprs/gtphub.c
+++ b/src/gprs/gtphub.c
@@ -1517,7 +1517,7 @@
 	int ie_mandatory = (p->type == GTP_CREATE_PDP_REQ);
 	unsigned int side_idx = p->side_idx;
 
-	for (plane_idx = 0; plane_idx < 2; plane_idx++) {
+	for_each_plane(plane_idx) {
 		int rc;
 		struct gsn_addr use_addr;
 		uint16_t use_port;