openflow_input: fix lengths in masked extension OXMs

The other backends don't rely on these lengths which is why this was never
noticed. The C backend relies on them, but used to set the length field for
OXMs itself.
diff --git a/openflow_input/bsn_global_vrf_allowed b/openflow_input/bsn_global_vrf_allowed
index 543c6fd..ee26308 100644
--- a/openflow_input/bsn_global_vrf_allowed
+++ b/openflow_input/bsn_global_vrf_allowed
@@ -41,7 +41,7 @@
 };
 
 struct of_oxm_bsn_global_vrf_allowed_masked : of_oxm {
-    uint32_t type_len == 0x00030701;
+    uint32_t type_len == 0x00030702;
     uint8_t value;
     uint8_t value_mask;
 };