io: fix setting of QIO_CHANNEL_FEATURE_FD_PASS on server connections

The QIO_CHANNEL_FEATURE_FD_PASS feature flag is set in the
qio_channel_socket_set_fd() method, however, this only deals
with client side connections.

To ensure server side connections also have the feature flag
set, we must set it in qio_channel_socket_accept() too. This
also highlighted a typo fix where the code updated the
sockaddr struct in the wrong object instance.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>