iw: Add support for NL80211_STA_INFO_RX_DURATION netlink attribute

iw: Add support for NL80211_STA_INFO_RX_DURATION netlink attribute

Add support for new netlink attribute 'NL80211_STA_INFO_RX_DURATION'.
'NL80211_STA_INFO_RX_DURATION' accounts for aggregate PPDU duration
in microseconds for all the frames from a peer. Drivers can fill
'rx_duration' field and set the flag 'NL80211_STA_INFO_RX_DURATION'.
'rx_duration' will give an idea about the total time spent by our peer
with each of its connected peers.

This will get dumped as part of 'iw dev wlan#N station dump'

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>