EHT requires that stations are able to participate in
wider bandwidth OFDMA, i.e. parse downlink OFDMA and
uplink OFDMA triggers when they're not capable of (or
not connected at) the (wider) bandwidth that the AP
is using. This requires hardware configuration, since
the entity responsible for parsing (possibly hardware)
needs to know the AP bandwidth.

To support this, change the channel request to have
the AP's bandwidth for clients, and track that in the
channel context in mac80211. This means that the same
chandef might need to be split up into two different
contexts, if the APs are different. Interfaces other
than client are not participating in OFDMA the same
way, so they don't request any AP setting.

Note that this doesn't introduce any API to split a
channel context, so that there are cases where this
might lead to a disconnect, e.g. if there are two
client interfaces using the same channel context, e.g.
both 160 MHz connected to different 320 MHz APs, and
one of the APs switches to 160 MHz.

Note also there are possible cases where this can be
optimised, e.g. when using the upper or lower 160 Mhz,
but I haven't been able to really fully understand the
spec and/or hardware limitations.

If, for some reason, there are no hardware limits on
this because the OFDMA (downlink/trigger) parsing is
done in firmware and can take the transmitter into
account, then drivers can set the new flag
IEEE80211_VIF_IGNORE_OFDMA_WIDER_BW on interfaces to
not have them request any AP bandwidth in the channel
context and ignore this issue entirely. The bss_conf
still contains the AP configuration (if any, i.e. EHT)
in the chanreq.

Link: https://msgid.link/20240129194108.d3d5b35dd783.I939d04674f4ff06f39934b1591c8d36a30ce74c2@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>