libnvmf: Improve handling of the CATTR field in CONNECT commands

[jhb]

Summary

• Add an association option to permit advertising support for I/O queue deletion in CATTR from the host side.

• When validating CONNECT commands in nvmf_accept(), validate the CATTR field rejecting non-zero values in reserved fields.

[jhb]

Neither the host nor controller sides in our NVMeoF bits support deleting individual I/O queues, so adding the new parameter is cosmetic (But needed if we ever had a compelling use case. I should probably implement support for it on the controller/target side at some point, but would need to be able to test it). However, validating that reserved fields aren't set is useful. I guess I can actually add some tests based on some recent tests I've started writing for nvmft at least, so I'll probably defer merging this until I can add some tests.