nl80211: Request kernel to trim off payload of netlink requests from acks

nl80211: Request kernel to trim off payload of netlink requests from acks

We do not need such payload in the acknowledgment, so adding it uses
resources unnecessarily. Furthermore, the original request can include
key material (e.g., NL80211_ATTR_PMK). libnl does not explicitly clear
this received message buffer and it would be inconvenient for
wpa_supplicant/hostapd to try to clear it with the current libnl design
where a duplicated buffer is actually passed to the callback. This means
that keys might be left unnecessarily in heap memory. Avoid this by
requesting the kernel not to copy back the request payload.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>