Add SPP (signaling and payload protected) AMSDU support.

Since userspace has to build the RSNX element, add an extended
feature flag to indicate that this is supported.

In order to avoid downgrade/mismatch attacks, add a flag to the assoc
command on the station side, so that we can be sure that the value of
the flag comes from the same RSNX element that will be validated by
the supplicant against the 4-way-handshake. If we just pulled the
data out of a beacon/probe response, we could theoretically look an
RSNX element from a different frame, with a different value for this
flag, than the supplicant is using to validate in the
4-way-handshake.

Note that this patch is only geared towards software crypto
implementations or hardware ones that can perfectly implement SPP
A-MSDUs, i.e. are able to switch the AAD construction on the fly for
each TX/RX frame.

For more limited hardware implementations, more capability
advertisement  would be required, e.g. if the hardware has no way
to switch this on the fly but has only a global configuration that
must apply to all stations.

The driver could of course *reject* mismatches, but the supplicant
must know so it can do things like not negotiating SPP A-MSDUs on
a T-DLS link when connected to an AP that doesn't support it, or
similar.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Daniel Gabay <daniel.gabay@intel.com>
Reviewed-by: Gregory Greenman <gregory.greenman@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240102213313.fadac8df7030.I9240aebcba1be49636a73c647ed0af862713fc6f@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>