kmod-sched-cake: fix parameter passing kernel/user space

The last two parameters passed between user space tc and kernel space
sched-cake were transposed due to a merge mistake in a parameter header
file.

As such, using a packet overhead figure was likely to set cake to wash
packet DSCP values.  Similarly, the DSCP wash flag was used as an offset
to the displayed packet overhead value.

Signed-off-by: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>