ceph: messenger: send banner in process_connect()

prepare_write_connect() has an argument indicating whether a banner
should be sent out before sending out a connection message.  It's
only ever set in one of its callers, so move the code that arranges
to send the banner into that caller and drop the "include_banner"
argument from prepare_write_connect().

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>