The feature here is a function to IGNORE RX for X milliseconds AFTER TX UNKEYS.
The rxondelay function is not sufficient due to the fact that it ignores rx audio independent if the transmitter has unkeyed or not. This causes audio cutoff when not necessary.
This is useful for linking simplex nodes to repeaters with a small squelch tail to prevent ping ponging.
Here is a better chan_usbradio.c that I just made which has added the function txoffdelay
Under usbradio.conf, please add txoffdelay=xxx where xxx is the number of 20ms intervals that you want to ignore RX only after TX UNKEY has occured.