Hi here is alternative method to install Injection driver,download from that link http://david.gnedt.eu/blog/wl1251/ first "Version 0.1 package including binary for kernel-power <= v49 (141mb) then "Version 0.2 binary build for kernel-power v50(1mb) to your pc,after downloading those files,connect your n900 witn pc(usb cable mass storage)transfer it to n900,then unplug usb cable open x-terminal:
sudo gainroot
cd MyDocs
mv wl1251-maemo-0.2-power49+pre50.tar.gz /home/user
tar -xzvf wl1251-maemo-0.1.tar.gz
cd ..
tar -xzvf wl1251-maemo-0.2-power49+pre50.tar.gz
cp wl1251-maemo/wl1251_spi.ko wl1251.ko rfkill_backport.ko mac80211.ko compat.ko cfg80211.ko /home/user/MyDocs/wl1251-maemo/binary/compat-wireless/
this is all,I am with kernel-power 50 and on this way until now,i no have any problems with Injection driver
regards