calidns: Add the --ecs parameter to add random ECS values to queries

[rgacogne]

Short description

This adds the possibility to simulate much more clients using calidns if the receiver is capable of handling the EDNS Client Subnet option.
The current code only supports IPv4, sorry about that.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled and tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[pieterlexis]

I had to read it a few times before I got it, but it is full of smarts 👍

[rgacogne]

Please tell me what you needed to read several times, it's probably lacking one (or more) comment!

[pieterlexis]

Please tell me what you needed to read several times, it's probably lacking one (or more) comment!

Mostly how the two new functions replace the bits in the IP addresses :).