flow: Clear ovs_nsh_key's context data when nsh's type can't be handled

In the default case when nsh's md_type is not recognized by nsh parser,
uninitialized data in key->context can sneak into miniflow. This
patch fixes it.

Reported-at: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=10519
Signed-off-by: Yifeng Sun <pkusunyifeng@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

lib/flow.c

@@ -576,6 +576,7 @@ parse_nsh(const void **datap, size_t *sizep, struct ovs_key_nsh *key)
             break;
         default:
             /* We don't parse other context headers yet. */
+            memset(key->context, 0, sizeof(key->context));
             break;
     }