ath11k: set DTIM policy to stick mode for station interface

Set DTIM policy to DTIM stick mode, so station follows AP DTIM
interval rather than listen interval which is set in peer assoc cmd.
DTIM stick mode is more preferred per firmware team request.

Tested-on: QCA6390 hw2.0 PCI WLAN.HST.1.0.1-01740-QCAHSTSWPLZ_V2_TO_X86-1

Signed-off-by: Carl Huang <quic_cjhuang@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/1638948694-15582-1-git-send-email-quic_cjhuang@quicinc.com