drivers: wifi: esp_at: fix last rx data loss in Passive Receive mode

In Passive Receive mode, ESP modem will buffer rx data.
This fix makes the data still available to user,
even though the peer has closed the socket.
Otherwise, user will fail to get the last rx data,
when the socket is closed by the peer.

Signed-off-by: Chun-Chieh Li <ccli8@nuvoton.com>