net: phy: Correctly handle MII ioctl which changes autonegotiation.

When advertised capabilities are changed with mii-tool, such as:
mii-tool -A 10baseT
the existing handler has two errors.

- An actual PHY register value is provided by mii-tool, and this
  must be mapped to internal state with mii_adv_to_ethtool_adv_t().
- The PHY state machine needs to be told that autonegotiation has
  again been performed.  If not, the MAC will not be notified of
  the new link speed and duplex, resulting in a possible config
  mismatch.

Signed-off-by: Brian Hill <Brian@houston-radar.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>