# DF-3595 — sc_curmac left NULL after failed band-switch/hw-reset while RUNNING: bwn_stop/bwn_detach/bwn_suspend NULL-deref panic

## Build / Run / Expected

```
# on the DF guest, as root:
sh probe.sh
```

Guest result: driver resident, **no Broadcom hardware** → runtime `inconclusive`.
On a BCM43xx machine: bring the interface up (firmware loads OK, RUNNING set),
then force `bwn_switch_band()`/`bwn_hwreset()` to fail — e.g. make
`bwn_core_init()` fail on re-init (unload the bwn v4 firmware files after first
bring-up, or flaky/malicious card) — then `ifconfig bwn0 down`, `devdetach`, or
suspend: `bwn_stop()` dereferences `sc->sc_curmac == NULL` at
`if_bwn.c:2048` → immediate kernel NULL-deref panic (`mac->mac_status` read at
address ~0x18).