tc: Add support for ce_threshold_value/mask in fq_codel

tc: Add support for ce_threshold_value/mask in fq_codel

Commit dfcb63ce1de6 ("fq_codel: generalise ce_threshold marking for subset
of traffic") added support in fq_codel for setting a value and mask that
will be applied to the diffserv/ECN byte to turn on the ce_threshold
feature for a subset of traffic.

This adds support to iproute for setting these values. The parameter is
called ce_threshold_selector and takes a value followed by a
slash-separated mask. Some examples:

 # apply ce_threshold to ECT(1) traffic
 tc qdisc replace dev eth0 root fq_codel ce_threshold 1ms ce_threshold_selector 0x1/0x3

 # apply ce_threshold to ECN-capable traffic marked as diffserv AF22
 tc qdisc replace dev eth0 root fq_codel ce_threshold 1ms ce_threshold_selector 0x50/0xfc

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: David Ahern <dsahern@kernel.org>