wifi: rtw88: usb: Update the RX stats after every frame

Update the number of received unicast data frames and bytes every time
a frame is received. This is what the PCI and SDIO drivers do.

This has an influence on the power saving, bluetooth coexistence, and
(in a future patch) the use of RX aggregation.

Tested with RTL8822CU, RTL8811CU, and RTL8723DU.

Tested-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/75a2ca52-8f01-45c5-926f-d3a68ae3b284@gmail.com