mlxsw: spectrum: Force link training according to admin state

When setting a new speed we need to disable and enable the port for the
changes to take effect. We currently only do that if the operational
state of the port is up. However, setting a new speed following link
training failure will require us to explicitly set the port down and then
up.

Instead, disable and enable the port based on its administrative state.

Fixes: 56ade8fe ("mlxsw: spectrum: Add initial support for Spectrum ASIC")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>