Reduce interrupt endpoint bInterval to 1ms polling

High-speed hosts compute bInterval differently. From my understanding,
this commit should result in a 1ms polling interval. The formula is

  Interval in microseconds = (2 ^ (bInterval - 1)) * 125us

This might resolve a contributor's observed warning during enumeration
(shown below). I was able to reproduce a similar warning on my own
system.

  [14381.332880] usb 1-4: config 1 interface 0 altsetting 0 endpoint
  0x81 has an invalid bInterval 255, changing to 11

That "changing to 11" results in a 128ms polling interval. I'm curious
if that's too slow.

src/cdc_acm.rs

@@ -54,7 +54,7 @@ impl<B: UsbBus> CdcAcmClass<'_, B> {
     pub fn new(alloc: &UsbBusAllocator<B>, max_packet_size: u16) -> CdcAcmClass<'_, B> {
         CdcAcmClass {
             comm_if: alloc.interface(),
-            comm_ep: alloc.interrupt(8, 255),
+            comm_ep: alloc.interrupt(8, 4),
             data_if: alloc.interface(),
             read_ep: alloc.bulk(max_packet_size),
             write_ep: alloc.bulk(max_packet_size),