When all the other drivers were converted to scheduling a taskqueue to

When all the other drivers were converted to scheduling a taskqueue to
do the heavy lifting of the 'mii_tick' function, rue was left behind.
Implement this in a naive way.  Reports from the field show this makes
the driver functional with some locking issues, as opposed to an
instant panic.  Those will be addressed in a later version of the
driver.

Approved by: re@ (bmah)