Disable usb status change and callback on SOF events

SOF events were introduced by the boot protocol changes, and required internally
by Zephyr's idle support, but are unused within ZMK itself. Ignore them in the
usb status callback.

app/src/usb.c

@@ -50,6 +50,12 @@ enum zmk_usb_conn_state zmk_usb_get_conn_state() {
 }
 
 void usb_status_cb(enum usb_dc_status_code status, const uint8_t *params) {
+    // Start-of-frame events are too frequent and noisy to notify, and they're
+    // not used within ZMK
+    if (status == USB_DC_SOF) {
+        return;
+    }
+
 #if IS_ENABLED(CONFIG_ZMK_USB_BOOT)
     if (status == USB_DC_RESET) {
         zmk_usb_hid_set_protocol(HID_PROTOCOL_REPORT);