usb: gadget: f_ncm: fix ncm_bitrate for SuperSpeed and above.

Currently, SuperSpeed NCM gadgets report a speed of 851 Mbps
in USB_CDC_NOTIFY_SPEED_CHANGE. But the calculation appears to
assume 16 packets per microframe, and USB 3 and above no longer
use microframes.

Maximum speed is actually much higher. On a direct connection,
theoretical throughput is about 3.86 Gbps for gen1x1 and
9.35 Gbps for gen2x1, and I have seen gadget->host speeds
>2 Gbps for gen1x1 and >4 Gbps for gen2x1.

Unfortunately the ConnectionSpeedChange defined in the CDC spec
only uses 32-bit values, so we can't report accurate numbers for
10Gbps and above. So always report a speed of 4 Gbps, which is
close enough to the technical maximum of a 5 Gbps link.

This results in:

[96033.958723] cdc_ncm 8-2:1.0 enx4643f5db6f40: renamed from usb0
[96033.997136] cdc_ncm 8-2:1.0 enx4643f5db6f40: 4000 mbit/s downlink 4000 mbit/s uplink

Fixes: 1650113 ("usb: gadget: f_ncm: add SuperSpeed descriptors for CDC NCM")
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>

drivers/usb/gadget/function/f_ncm.c

@@ -85,8 +85,8 @@ static inline struct f_ncm *func_to_ncm(struct usb_function *f)
 /* peak (theoretical) bulk transfer rate in bits-per-second */
 static inline unsigned ncm_bitrate(struct usb_gadget *g)
 {
-	if (gadget_is_superspeed(g) && g->speed == USB_SPEED_SUPER)
-		return 13 * 1024 * 8 * 1000 * 8;
+	if (gadget_is_superspeed(g) && g->speed >= USB_SPEED_SUPER)
+		return 4000000000;
 	else if (gadget_is_dualspeed(g) && g->speed == USB_SPEED_HIGH)
 		return 13 * 512 * 8 * 1000 * 8;
 	else