wifi: nl80211: add RX and TX timestamp attributes

Add attributes for reporting hardware timestamps for management frames
RX and TX. These attributes will be used for reporting hardware
timestamps for Timing measurement and Fine Timing Measurement action
frames, which will allow userspace applications to measure the path
delay between devices and sync clocks.

For TX, these attributes are used for reporting the frame RX time and
the ack TX time. For TX, they are used for reporting the frame TX time
and the ack RX time.

Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>