- create one taskqgroup for rx and tx
- handle initialization of flowid, hash_type, csum_data, csum_flags, and
  vlan tag in the packet header
- track pktlen in packet header in case of multi-fragment packet
- poll txq for completions if necessary before cleaning
- pass a driver determined argument to device filters
- don't bind config queues to cpus
- add iflib_taskqgroup_attach for drivers to specify their own config
  tasks
convert to iflib interface