obfs2 should wait before closing connection on wrong magic/plength

...
If the MAGIC_VALUE does not match, or the PADLEN value is greater
than MAX_PADDING, the party receiving it should wait for a random
amount of time then close the connection.
...

says the spec.

...
if (magic != OBFUSCATE_MAGIC_VALUE)
     return -1;
...

says the source.

The spec also doesn't specify the time interval that we should be randomly waiting.