src: extend nft to list object handle and delete objects via handle

src: extend nft to list object handle and delete objects via handle

Print handle attributes in objects when listing via '-a' option and
delete objects via their unique object handles.
For e.g.

nft delete [<object-type>] [<family>] <table-name> [handle <handle>]

Signed-off-by: Harsha Sharma <harshasharmaiitr@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>