PowerDNS sdig does not truncate trailing bits of EDNS Client Subnet mask

[ahupowerdns]

So if you'd truncate something as
a /9, we'd have to use 2 bytes anyhow, but we would not zero the last 7 bits.

We do now. Thanks Mukund & ISC!

Short description

Use ComboAddress::truncate logic.

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)
• checked that this code was merged to master

[rgacogne]

Every single unit test falls on a byte boundary.. I'll have to add some to cover this case.