USB: Expose vendor-specific ACM channel on Nokia 5230

Nokia S60 phones expose two ACM channels. The first is
a modem, the second is 'vendor-specific' but is treated
as a serial device at the S60 end, so we want to expose
it on Linux too.

Signed-off-by: Przemo Firszt <przemo@firszt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>