ath10k: clean up assoc code

There's no need to pass bss_conf explicitly as it
is accessible via vif pointer. This requires
slight changes in function prototypes. While at it
clean up listen interval workaround/command.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>