net: dsa: do not call phy_start_aneg

Commit f7f1de51 ("net: dsa: start and stop the PHY state machine")
add calls to phy_start() in dsa_slave_open() respectively phy_stop() in
dsa_slave_close().

We also call phy_start_aneg() in dsa_slave_create(), and this call is
messing up with the PHY state machine, since we basically start the
auto-negotiation, and later on restart it when calling phy_start().
phy_start() does not currently handle the PHY_FORCING or PHY_AN states
properly, but such a fix would be too invasive for this window.

Fixes: f7f1de51

 ("net: dsa: start and stop the PHY state machine")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>