Add support for setting ToS bits with ping/fping

Ping (-Q) and fping (-O) supports setting the Type-of-Service (ToS) bits
the quality-of-service related bits in ICMP datagrams.

This is useful for e.g. testing the priority bands of the pfifo_fast
or prio qdisc.

Original patch by Dave Taht.

Original-by: Dave Taht <dave.taht@bufferbloat.net>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
tests: rrul_prio - Add explicit support for testing some prioritization only

This test "rrul_prio" will set the ToS fields on some of the latency tests,
which is useful for testing the priority bands of pfifo_fast and prio qdiscs.

Signed-off-by: Dave Taht <dave.taht@bufferbloat.net>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>