q_cake: Fix incorrect printing of signed values in class statistics

q_cake: Fix incorrect printing of signed values in class statistics

The deficit returned from the kernel is signed, but was printed with a %u
specifier in the format string, leading to negative values to be printed as
high unsigned values instead. In addition, we passed a negative value to
sprint_time() even though that expects an unsigned value. Fix this by
changing the format specifier and reversing the sign of negative time
values.

Fixes: 714444c0cb26 ("Add support for CAKE qdisc")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>