re-enabling if_bwi

[Jost Tobias Springenberg <k-gee@xxxxxxx>]

Hi,
since I had a few hours of free coding time at hand last night and was
in need of a wlan card for a server, I decided to try bringing the
if_bwi driver back into head.

I therefore backported the changes from freebsd and changed the
locking procedure to use the wlan_serialize calls. 
Right now the module compiles and can be loadded correctly. The
firmware is however not loaded / found.
Does anyone Have a pointer to what I might be doing wrong there ?

The changes I made are attached as patch files, if anyone else wants to
try them.

Greetings,
Tobias