wimax/i2400m: Add support for more i6x50 SKUs

The Intel WiMax Wireless Link 6050 can show under more than one USB
ID. Add support for all, introducing a generic flag (i2400mu->i6050)
that denotes a 6x50 based device.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>