[iwn] Centrino 135 support

[Gavin Atkinson]

Hi all,

I have a new laptop (Lenovo G500s) with a Centrino 135, which isn't 
currently supported by iwn(4).  According to the Linux driver, this 
chipset requires a new firmware, but otherwise appears to be treated very 
similarly to the 2030.

The patch at http://people.freebsd.org/~gavin/iwn135.diff works for me.  
I've tested it heavily with a IWN_DID_135_2/IWN_SDID_135_2 device on both 
11g and 11ng, and it seems stable (certainly no less stable than other 
iwn(4) interfaces...)

Is anybody able to review?

Thanks,

Gavin