Drivers may need to validate configuration of a device that's about to
be upped. Should the validation fail, there's currently no way to
communicate details of the failure to the user, beyond an error number.

To mend that, change __dev_open() to take an extack argument and pass it
from __dev_change_flags() and dev_open(), where it was propagated in the
previous patches.

Change __dev_open() to call call_netdevice_notifiers_extack() so that
the passed-in extack is attached to the NETDEV_PRE_UP notifier.
Signed-off-by: Petr Machata <petrm@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>