rigth crc32 implementation

Hi,

Working on usb_adslsubr{.c,.h}

About how to implement crc32

My first think was use the libkern based one, but I found:
sys/linkern/crc32.c

- the code may not be endian safe.
- the code lacks support for processing chuncks.

Add the functions for the second target may be easy (please, sugest 
names), but I found a latest problem:

At last geom uses this to sign data structures.  If the code is made 
endian safe, this will break geom.

At the moment, I'll work this into usb_adslsubr{.c,.h}, but I'll glad to 
know if those targets will be wellcome.

--
  josemi