mvswitch: fix autonegotiation issue

mvswitch: fix autonegotiation issue

The Marvel 88E6060 switch has an MDIO interface, but does not emulate
regular PHY behavior for the host. The network core can not detect using
the generic code, whether the connection via the attached PHY can be
used or not. The PHY's state machine is stuck in a state of
auto-negotiation and does not go any further so the Ethernet interface
of the router stay forever in the not-runing state.

Fix this issue by implementing the aneg_done callback to be able to
inform the network core that the Ethernet interface link to which the
switch is connected can be marked as RUNNING.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>