nl80211: add scan width to bss and scan request structs

To allow scanning and working with 5 MHz and 10 MHz BSS, extend the
inform bss commands and add wrappers to take 5 and 10 MHz bss into
account.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>