MAJOR: connection: move the addr field from the stream_interface

MAJOR: connection: move the addr field from the stream_interface

We need to have the source and destination addresses in the connection.
They were lying in the stream interface so let's move them. The flags
SI_FL_FROM_SET and SI_FL_TO_SET have been moved as well.

It's worth noting that tcp_connect_server() almost does not use the
stream interface anymore except for a few flags.

It has been identified that once we detach the connection from the SI,
it will probably be needed to keep a copy of the server-side addresses
in the SI just for logging purposes. This has not been implemented right
now though.