[SPARC64]: Fix race between MD update and dr-cpu add.

We need to make sure the MD update occurs before we try to
process dr-cpu configure requests.  MD update and dr-cpu
were being processed by seperate threads so that did not
happen occaisionally.

Fix this by executing all domain services data packets from
a single thread, in order.

This will help simplify some other things as well.

Signed-off-by: David S. Miller <davem@davemloft.net>