ofp-meter: Fix use-after-free for decoding meter mods.

ofputil_pull_bands() may change bands->data.

Found by libfuzzer-ngram.

Reported-by: Bhargava Shastry <bshastry@sect.tu-berlin.de>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Reviewed-by: Yifeng Sun<pkusunyifeng@gmail.com>

lib/ofp-util.c

@@ -1863,12 +1863,12 @@ ofputil_decode_meter_mod(const struct ofp_header *oh,
             mm->meter.flags & OFPMF13_PKTPS) {
             return OFPERR_OFPMMFC_BAD_FLAGS;
         }
-        mm->meter.bands = bands->data;
 
         error = ofputil_pull_bands(&b, b.size, &mm->meter.n_bands, bands);
         if (error) {
             return error;
         }
+        mm->meter.bands = bands->data;
     }
     return 0;
 }