net: devlink: enable parallel ops on netlink interface

As the devlink_mutex was removed and all devlink instances are protected
individually by devlink->lock mutex, allow the netlink ops to run
in parallel and therefore allow user to execute commands on multiple
devlink instances simultaneously.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>