ipv4: add test for ipv4.dhcp-dscp
Test that the values passed via ipv4.dhcp-dscp
take effect. Note
that the property only works with the internal client at the
moment.
Test the 3 supported values: CS6 (default), CS4, CS0. Check that the right DSCP value is set in: the DHCP DISCOVER, the DHCP REQUEST and when renewing the lease, as this last case uses a different socket (UDP instead of packet socket).
https://issues.redhat.com/browse/RHEL-16040 NetworkManager!1824 (merged)