mlxsw: spectrum_acl: Allow to get group_id value for a ruleset

For goto_chain action we need to know group_id of a ruleset to jump to.
Provide infrastructure in order to get it.

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