The spec requires them to do so, and not doing so creates a situation
where they can't send-test because relays won't extend to them because
of the other part of bug 9546.
Fixes bug 9546; bugfix on 0.2.3.6-alpha.
Relays previously, when initiating a connection, would only send a
NETINFO after sending an AUTHENTICATE. But bridges, when receiving a
connection, would never send AUTH_CHALLENGE. So relays wouldn't
AUTHENTICATE, and wouldn't NETINFO, and then bridges would be
surprised to be receiving CREATE cells on a non-open circuit.
Fixes bug 9546.