[SPARC64] sunhv: Fix locking in sunhv_start_tx()

Caller takes the lock already.

Also, fixup the poll loop in sunhv_break_ctl().  Just
like in console write, we udelay(2) and use a loop
limit of 1000000 iterations.

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