iflib's generic device-deregister path never drains the admin task
before calling IFDI_DETACH, so bnxt_update_admin_status() (scheduled
once/sec) could still run concurrently with bnxt_detach(), racing on
softc->hwrm_lock and the shared HWRM request/response DMA buffer that
bnxt_detach() destroys. That race could leave the firmware-side HWRM
mailbox inconsistent, surfacing as "Timeout sending HWRM_VER_GET" on
the next module load.
Add a softc->detached guard: set it as the first statement in
bnxt_detach(), and bail out of bnxt_update_admin_status() immediately
when it's set.