Avoid "mac clock not ready" panic in iwx(4).

Avoid "mac clock not ready" panic in iwx(4).

The same change was just made in iwm(4):

The point of iwm_nic_assert_locked() is to verify that iwm_nic_lock() has
been called somewhere up in the call stack. Checking our own lock counter
is sufficient for this purpose.

If locking the device worked then these registers had the expected state at
that time and our lock counter was incremented. Apparently if the device runs
into some issue later the state of these registers may change and trigger
these panics. Instead we want to handle such failures gracefully and reset
the device.

problem reported by steven@
ok kettenis@