nl80211: Add FILS discovery support

FILS discovery attribute, NL80211_ATTR_FILS_DISCOVERY, is nested which
supports following parameters as given in IEEE Std 802.11ai-2016,
Annex C.3 MIB detail:
(1) NL80211_FILS_DISCOVERY_ATTR_INT_MIN - Minimum packet interval
(2) NL80211_FILS_DISCOVERY_ATTR_INT_MAX - Maximum packet interval
(3) NL80211_FILS_DISCOVERY_ATTR_TMPL - Template data

Signed-off-by: Aloka Dixit <alokad@codeaurora.org>
Link: https://lore.kernel.org/r/20200805011838.28166-2-alokad@codeaurora.org
[fix attribute and other names, use NLA_RANGE(), use policy only once]
Link: https://lore.kernel.org/r/010101747a7b38a8-306f06b2-9061-4baf-81c1-054a42a18e22-000000@us-west-2.amazonses.com


Signed-off-by: Johannes Berg <johannes.berg@intel.com>