cfg80211: support RNR for EMA AP

As per IEEE Std 802.11ax-2021, 11.1.3.8.3 Discovery of a nontransmitted
BSSID profile, an EMA AP that transmits a Beacon frame carrying a partial
list of nontransmitted BSSID profiles should include in the frame
a Reduced Neighbor Report element carrying information for at least the
nontransmitted BSSIDs that are not present in the Multiple BSSID element
carried in that frame.
Add new nested attribute NL80211_ATTR_EMA_RNR_ELEMS to support the above.
Number of RNR elements must be more than or equal to the number of
MBSSID elements. This attribute can be used only when EMA is enabled.
Userspace is responsible for splitting the RNR into multiple elements such
that each element excludes the non-transmitting profiles already included
in the MBSSID element (%NL80211_ATTR_MBSSID_ELEMS) at the same index.
Each EMA beacon will be generated by adding MBSSID and RNR elements
at the same index. If the userspace provides more RNR elements than the
number of MBSSID elements then these will be added in every EMA beacon.

Signed-off-by: Aloka Dixit <quic_alokad@quicinc.com>
Link: https://lore.kernel.org/r/20230323113801.6903-2-quic_alokad@quicinc.com


[Johannes: validate elements]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>