This patch adds the dev_id field in the control structure, to
identify different devices driven by the same driver, when the bus
abstraction will be completed.

Fields are also reordered: now hostid, devname, dev_id, cset_i and
chan_i are consecutive; thus, they can defined as a sockaddr_zio
structure for the forthcoming PF_ZIO infrastructure, without changing
the control structure again.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
Acked-by: Federico Vaga <federico.vaga@gmail.com>