nl80211: add support for BSSIDs in scheduled scan matchsets

This patch allows for the scheduled scan request to specify matchsets
for specific BSSIDs.

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>
[docs, netlink policy fix]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>