reduce the delays used in the mii/mdio bus ops

reduce the delays used in the mii/mdio bus ops

this produces a significant speed up.

say you're reading 40ish mib counters off a port on switch chip,
where each counter read relies on multiple mdio operations. it took
well over a second to read the counters off a port in my my initial
version. after optimising the switch reads i got that down to a bit
under a second. after this change in dwqe i can read counters off
5 ports in about 0.03 seconds.

ok patrick@