iwlwifi: pcie: properly set LTR workarounds on 22000 devices

As the context info gen3 code is only called for >=AX210 devices
(from iwl_trans_pcie_gen2_start_fw()) the code there to set LTR
on 22000 devices cannot actually do anything (22000 < AX210).

Fix this by moving the LTR code to iwl_trans_pcie_gen2_start_fw()
where it can handle both devices. This then requires that we kick
the firmware only after that rather than doing it from the context
info code.

Note that this again had a dead branch in gen3 code, which I've
removed here.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Fixes: ed0022da ("iwlwifi: pcie: set LTR on more devices")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20210326125611.675486178ed1.Ib61463aba6920645059e366dcdca4c4c77f0ff58@changeid