ospfd: fix "show ip ospf database" issues

ospfd: fix "show ip ospf database" issues

Current implementation of commands `show_ip_ospf_instance_database_cmd`
and `show_ip_ospf_instance_database_type_adv_router_cmd` have the
following problems:

- they doesn't have "vrf all" argument, however the processing of this
  argument is implemented,

- they incorrectly implement json output for instances - they don't
  output anything to the vty and don't release the json object.

To fix the problems, let's do the following:

1. Split `show_ip_ospf_instance_database_cmd` into two aliases to
   `show_ip_ospf_database_max_cmd` and `show_ip_ospf_instance_database_max_cmd`.
   The code is the same and doesn't need to be duplicated.

2. Split `show_ip_ospf_instance_database_type_adv_router_cmd` into two
   separate functions - one regular and one for instances, which now
   correctly implements the processing for json output.

Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>