nimble/controller: Ignore scan rsp which is not an answer on scan req
nimble/controller: Ignore scan rsp which is not an answer on scan req

According to spec in active scan we should listend for advertising pdu's
and when doing scan request we should listen for scan rsp. Otherwise we
should not care about scan rsp.

One of the issue due to this is following scenario:
* user put device a into white list
* user enable active scan with white list

result:
If more devices around, user got notification on scan response from
devices not in the wl

X-Original-Commit: 2a36552518a790614c1951f13fe8f663bad5e9e0

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble