Minor bugfix to spgw.p4

Change-Id: I2668883ba73558d445f05b7d2e3901252b5a640c
diff --git a/pipelines/fabric/src/main/resources/include/header.p4 b/pipelines/fabric/src/main/resources/include/header.p4
index 7b61cec..6cff586 100644
--- a/pipelines/fabric/src/main/resources/include/header.p4
+++ b/pipelines/fabric/src/main/resources/include/header.p4
@@ -133,6 +133,7 @@
 struct spgw_meta_t {
     bool              do_spgw;
     direction_t       direction;
+    bit<16>           ipv4_len;
     bit<32>           teid;
     bit<32>           s1u_enb_addr;
     bit<32>           s1u_sgw_addr;