Feature request: Add DSCP/ToS marking support

[aybru]

Feature request: add DSCP/ToS marking support.

• Add a CLI flag or config option to set DSCP value (e.g., 46 for EF)
• Apply to all outgoing DNS traffic: plain DNS, DoT, DoH, etc.
• Useful for QoS setups with Linux qdisc (CAKE, fq_codel) to prioritize DNS
• More reliable than port/process-based iptables/nftables marking

Thank you!