ath11k: Handle keepalive during WoWLAN suspend and resume

With WoWLAN enabled and after sleeping for a rather long time,
we are seeing that with some APs, it is not able to wake up
the STA though the correct wake up pattern has been configured.
This is because the host doesn't send keepalive command to
firmware, thus firmware will not send any packet to the AP and
after a specific time the AP kicks out the STA.

Fix this issue by enabling keepalive before going to suspend
and disabling it after resume back.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-01720.1-QCAHSPSWPL_V1_V2_SILICONZ_LITE-1

Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220506012540.1579604-1-quic_bqiang@quicinc.com