ixl(4)'s nvmupdate utility expects the nvmupdate process to run
while the interface is down; these nvm update commands use the
admin queue, so the admin queue needs to be able to generate
interrupts and be processed while the interface is down.

So add a flag that ixl(4) sets that lets the entire admin task
run even when the interface is marked down/IFF_DRV_RUNNING isn't set.

With this change, nvmupdate should function like it did pre-iflib.