Loxigen: added src/dst meta id matches

Encode a 1 byte src and 1 byte dst 'meta' ID into
ofp_match's pad2 byte.
diff --git a/openflow_input/oxm-1.2 b/openflow_input/oxm-1.2
index b18c6fb..37737c1 100644
--- a/openflow_input/oxm-1.2
+++ b/openflow_input/oxm-1.2
@@ -433,3 +433,25 @@
     uint16_t value;
     uint16_t value_mask;
 };
+
+struct of_oxm_src_meta_id {
+    uint32_t type_len == 0x0003f001;
+    uint8_t value;
+};
+
+struct of_oxm_src_meta_id_masked {
+    uint32_t type_len == 0x0003f102;
+    uint8_t value;
+    uint8_t value_mask;
+};
+
+struct of_oxm_dst_meta_id {
+    uint32_t type_len == 0x0003f201;
+    uint8_t value;
+};
+
+struct of_oxm_dst_meta_id_masked {
+    uint32_t type_len == 0x0003f302;
+    uint8_t value;
+    uint8_t value_mask;
+};