cxgbe(4): Do not report link state change during interface detach.

[np]

Summary

This fixes a panic when multiple VIs are configured on an interface and
only the non-primary VI is up at the time of drive detach. The problem
was that the driver would queue a link state change notification for an
interface about to be freed.

To reproduce the panic, add "hw.cxgbe.num_vis=2" to loader.conf and

1. kldload if_cxgbe
2. ifconfig vcc0 up
3. devctl detach t6nex0
   • trap 0x9, rip = 0xffffffff8107db70, rsp = 0xfffffe0055263d60, rbp = 0xfffffe0055263dd0 --- taskqueue_run_locked() at taskqueue_run_locked+0x2a0/frame 0xfffffe0055263dd0 taskqueue_run() at taskqueue_run+0x72/frame 0xfffffe0055263df0 taskqueue_swi_run() at taskqueue_swi_run+0x18/frame 0xfffffe0055263e10 intr_event_execute_handlers() at intr_event_execute_handlers+0x249/frame 0xfffffe0055263e50 ithread_execute_handlers() at ithread_execute_handlers+0x9e/frame 0xfffffe0055263e70

MFC after: 1 week
Sponsored by: Chelsio Communications

[jhb]

sys/dev/cxgbe/t4_main.c

12115

I don't think vi can ever be NULL here. I'm also not a super fan of assignment side effects inside of if statements, so I would probably just add:

if (IS_DETACHING(vi)
   continue;

before the existing check, or maybe

if (ifp == NULL || IS_DETACHING(vi))
   continuel

[np]

Incorporate feedback from jhb.