netem: use 64 bit value for latency and jitter

netem: use 64 bit value for latency and jitter

The current version of netem in iproute2 has a maximum of 4.3 seconds
because of scaled 32 bit clock values. Some users would like to be
able to use larger delays to emulate things like storage delays.

Since kernel version 4.15, netem qdisc had netlink parameters
to express wider range of delays in nanoseconds. But the iproute2
side was never updated to use them.

This does break compatibility with older kernels (4.14 and earlier).
With these out of support kernels, the latency/delay parameter
will end up being ignored.

Reported-by: Marc Blanchet <marc.blanchet@viagenie.ca>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>