wifi: rtw89: wow: send ARP reply packets instead of Null packets to keep alive

wifi: rtw89: wow: send ARP reply packets instead of Null packets to keep alive

In WoWLAN mode, the firmware periodically sends Null packets to the AP
to keep the connection alive and prevent the AP from disconnecting the
client due to inactivity. However, it was observed that certain APs,
such as  TP-Link Archer BE800, do not recognize Null packets as
valid activity and still drop the connection. Replacing Null packets
with ARP reply packets effectively resolves this compatibility issue
and maintains the connection.

Specifically, while the firmware typically handles standard ARP
offloads by dynamically modifying target IP/MAC fields, these
keep-alive ARP reply packets are pre-filled by the driver with the
DUT's own MAC and IP addresses for both sender and target fields.
In this case, the firmware transmits the packets as-is without
further modification. This approach ensures compatibility with APs
that require valid Layer 3 traffic for activity monitoring while
simplifying the firmware's processing logic during WoWLAN mode.

Signed-off-by: Chin-Yen Lee <timlee@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20260515014433.16168-9-pkshih@realtek.com