wifi: mac80211: hide element parsing internals

Rework the data structures to hide element parsing internals
from the users.

Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240228094902.19c610b529e2.Ie7ea2dcb6713911590ace6583a4748f32dc37df2@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

wifi: mac80211: remove unneeded scratch_len subtraction

We're always using "scratch + len - pos", so we don't need
to subtract here to calculate the remaining length. Remove
the unnecessary subtraction.

Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Reviewed-by: Ilan Peer <ilan.peer@intel.com>
Link: https://msgid.link/20240228094902.44e07cfa9e63.I7a9758fb9bc6b726aac49804f2f05cd521bc4128@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

wifi: mac80211: defragment reconfiguration MLE when parsing

Using the scratch buffer (without advancing it) here in the
mlme.c code seems somewhat wrong, defragment the reconfig
multi-link element already when parsing. This might be a bit
more work in certain cases, but makes the whole thing more
regular.

Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240228094902.92936a3ce216.I4b736ce4fdc199fa1d6b00d00032f448c873a8b4@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

wifi: mac80211: simplify multi-link element parsing

We shouldn't assign elems->ml_basic{,len} before defragmentation,
and we don't need elems->ml_reconf{,len} at all since we don't do
defragmentation. Clean that up a bit. This does require always
defragmention even when it may not be needed, but that's easier
to reason about.

Reviewed-by: Ilan Peer <ilan.peer@intel.com>
Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240228094902.e0115da4d2a6.I89a80f7387eabef8df3955485d4a583ed024c5b1@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

wifi: mac80211: remove unnecessary ML element checks

Given the prior changes to ieee80211_mle_size_ok(), we
can now pass NULL to for_each_mle_subelement(), so no
longer need to check for that here explicitly.

Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240228094901.9e32c4b63875.Ia2ee0aafdc8a48bd21b485cc36a9866f950d781b@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

wifi: mac80211: remove unnecessary ML element type check

At this point, since it's taken from elems->ml_basic which
is stored only if it's of type basic, we don't really need
to check again if it's basic.

Reviewed-by: Ilan Peer <ilan.peer@intel.com>
Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240228094901.ad1d4a09a6eb.Ib96fa75b1a6db21dd4182dcfa11fe9aff78fa3ed@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

wifi: mac80211: update scratch_pos after defrag

The scratch_pos update here was lost after defrag, so any
other uses of the scratch buffer might overwrite it.

Fixes: a286de1aa38f ("wifi: mac80211: Rename multi_link")
Reviewed-by: Benjamin Berg <benjamin.berg@intel.com>
Reviewed-by: Ilan Peer <ilan.peer@intel.com>
Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240228094901.9da35f39eeb7.I7127f2918ec4cba416fcbc35eacaea10262c1268@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

wifi: mac80211: move element parsing to a new file

This code got really big, move it to a new file.
Pure code move.

Link: https://msgid.link/20240129202041.7f27f7c895e4.I0adfc28bd656a4d44c2bf47966277eecf56cbaa0@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>