kern/72935: sio tty and uhid tty (perhaps others) stomp on each other leading to kernel data corruption and a panic

[Keith Winter]

We are trying to generalize the fix for this.  It was pointed out by Julian Elischer that this prevents bio devices from trampling
on tty devices, but not vice versa.

Would the following be a more general solution for uhid devices?

        {
                int s = splhigh();
                tty_imask |= bio_imask;
                bio_imask |= tty_imask;
                update_intr_masks();
                splx( s );
        }

The approach is similar to what was done for ppp/slip.

-- KDW