BGP: Fix update-groups commands to match neighbors

BGP: Fix update-groups commands to match neighbors

show update-groups summary was mislabeled. What it displays is not a summary
at all, but the detailed info about all update-groups. Furthermore, there
was no way to get detailed info about a specific subgroup.

This patch renames "show * update-groups summary" to "show * update-groups"
and adds an option to see the info specific to a subgroup only. It also
validates the subgroup-id.

show * update-groups summary will be added separately.