nl80211/cfg80211: Extended Key ID support

Add support for IEEE 802.11-2016 "Extended Key ID for Individually
Addressed Frames".

Extend cfg80211 and nl80211 to allow pairwise keys to be installed for
Rx only, enable Tx separately and allow Key ID 1 for pairwise keys.

Signed-off-by: Alexander Wetzel <alexander@wetzel-home.de>
[use NLA_POLICY_RANGE() for NL80211_KEY_MODE]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>