This is the function that should be called regardless of
TCP or TLS being used. The proper usage for this function is:

{ok, ProxyInfo} = ranch:recv_proxy_header(Ref, Timeout),
{ok, Socket} = ranch:handshake(Ref),
...

Ranch takes care of everything else under the hood. Transports
now need to have a Transport:recv_proxy_header/2 function. For
ranch_ssl the function gets the port from the sslsocket() record
and then calls ranch_tcp:recv_proxy_header/2 with it.

This means that two undocumented features are currently used for
this, but the interface is really nice so that's a sacrifice
worth doing. Also worth noting is that OTP 22 should have an
alternative for gen_tcp:unrecv/2 so the only real issue is about
the sslsocket() record at the moment.

The race condition occurs when the restart is faster than
the cleaning up. With this commit the restart will perform
the cleanup if it was not done beforehand.

This uses the undocumented function gen_tcp:unrecv/2.

Tests have been added for both gen_tcp and ssl connections,
including sending data in the same first packet, at least
for gen_tcp (ssl tests may or may not end up buffering some
of the TLS handshake before the recv call, but there's no
guarantees).

I had to use the process dictionary to work around the current
interface for one log call. You have been warned.