Feature request: control `op` to send

[michele]

Hello folks!

It would be fantastic if drill would allow customizing the optype to send, similar to what dig does. In particular, this would allow using drill to test NOTIFY queries:

dig @1.2.3.4 nlnetlabs.nl soa +norecurse +aa +opcode=notify

drill gets incredibly close with this command:

drill @1.2.3.4 nlnetlabs.nl SOA -o rd -o AA

... but currently lacks the ability to set the opcode in the header.

Regardless if you choose to pick up this feature or not, thanks for all you did at NLnetLabs so far!