iwlwifi: mvm: Use aux queue for offchannel frames in dqa

Since offchannel activity doesn't always require a BSS, e.g. ANQP
sessions, offchannel frames should not use the BSS queue, because it
might not be initialized.
Use the auxilary queue instead

Fixes: e3118ad7 ("iwlwifi: mvm: support tdls in dqa mode")
Signed-off-by: Beni Lev <beni.lev@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>