ofp-util: Actually map vendor codes to IDs correctly.

Reported-by: Justin Pettit <jpettit@nicira.com>

lib/ofp-util.c

@@ -829,6 +829,8 @@ vendor_code_to_id(uint8_t code)
 {
     switch (code) {
 #define OFPUTIL_VENDOR(NAME, VENDOR_ID) case NAME: return VENDOR_ID;
+        OFPUTIL_VENDORS
+#undef OFPUTIL_VENDOR
     default:
         return UINT32_MAX;
     }