obfsproxy: Use server-side transport parameters
A client-side obfsproxy can get transport parameters by using the SOCKS handshake username/password fields.
On the server-side obfsroxy should use the scheme from #8929 (moved) to get the transport parameters. Also, after using them, obfsproxy should send the parameters that must be advertised in the extra-info descriptor using the ARGS
option in the SMETHOD
line.