USB: Support for the ET502HS HDSPA modem in option driver

the proposed patch allows the ET502HS HDSPA modem to be handled by the
"option" driver. It has been tested for 1 month and works reliably (no
oopses, no hangs, 300KB/s throughput).

Signed-off-by: Mauro Andreolini <andreoli@weblab.ing.unimo.it>
Signed-off-by: Matthias Urlichs <matthias@urlichs.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>