Integer overflow in cafe http stream

[requilence]

Describe the bug
When a cafe tries to send the payload larger than uint16(65535) length, it overflows the size bytes here. As a result, a client is got unexpected EOF when trying to unmarshal into pb.Envelope here

To Reproduce

1. Create a lot of peers for an account
2. Do SearchContacts, providing this account's address

Expected behavior
Got accounts as usual

I'm not sure what is a good way to fix this while preserving backward compatibility.
Here is what I have in mind

• increase the length of size bytes to 4, but only for textile user agents higher than X version
• add an extra param to the query with the length of size bytes prefix. Use 2 by default

Let me know what do you think do so I can provide PR