wifi: rtw88: usb: Support RX aggregation

The chips can be configured to aggregate several frames into a single
USB transfer. Modify rtw_usb_rx_handler() to support this case.

RX aggregation improves the RX speed of RTL8811CU on certain ARM
systems, like the NanoPi NEO Core2. It also improves the RX speed of
RTL8822CU on some x86_64 systems.

Currently none of the chips are configured to aggregate frames.

Tested with RTL8822CU, RTL8811CU, and RTL8723DU.

Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
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/f845826d-de71-492d-9a22-e48c07989a1f@gmail.com