Fixed typo in usb-send-delay-threshold on the man page

Author: alexpevzner

ipp-usb.8

@@ -320,7 +320,7 @@ Don't use more that N USB interfaces, even if more is available\.
 .br
 Delay between low\-level USB send\-to\-device requests (this is not the same as \fBrequest\-delay\fR, which inserts delays between the whole HTTP\-level requests)\.
 .IP "\(bu" 4
-\fBusb\-send\-delay\-threshold = DELAY\fR
+\fBusb\-send\-delay\-threshold = N\fR
 .br
 \fBusb\-send\-delay\fR only applied if USB send\-to\-device request size exceeds this threshold\.
 .IP "\(bu" 4

ipp-usb.8.md

@@ -407,7 +407,7 @@ The following parameters are defined:
      the same as `request-delay`, which inserts delays between the
      whole HTTP-level requests).
 
-   * `usb-send-delay-threshold = DELAY`<br>
+   * `usb-send-delay-threshold = N`<br>
      `usb-send-delay` only applied if USB send-to-device request size
      exceeds this threshold.