devlink: parse linecard attr in doit() callbacks

No need to give the linecards any special treatment in netlink attribute
parsing, as unlike for ports, there is only a couple of commands
benefiting from that.

Remove DEVLINK_NL_FLAG_NEED_LINECARD, make pre_doit() callback simpler
by moving the linecard attribute parsing to linecard_[gs]et_doit() ops.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20230811155714.1736405-2-jiri@resnulli.us


Signed-off-by: Jakub Kicinski <kuba@kernel.org>