wifi: iwlwifi: mvm: disable MLO for the time being

MLO ended up not really fully stable yet, we want to make
sure it works well with the ecosystem before enabling it.
Thus, remove the flag, but set WIPHY_FLAG_DISABLE_WEXT so
we don't get wireless extensions back until we enable MLO
for this hardware.

Cc: stable@vger.kernel.org
Reviewed-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240314110951.d6ad146df98d.I47127e4fdbdef89e4ccf7483641570ee7871d4e6@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>