cfg80211: add request id to cfg80211_sched_scan_*() api

Have proper request id filled in the SCHED_SCAN_RESULTS and
SCHED_SCAN_STOPPED notifications toward user-space by having the
driver provide it through the api.

Reviewed-by: Hante Meuleman <hante.meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Reviewed-by: Franky Lin <franky.lin@broadcom.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>