src: add set_is_datamap(), set_is_objmap() and set_is_map() helpers

src: add set_is_datamap(), set_is_objmap() and set_is_map() helpers

Two map types are currently possible:

* data maps, ie. set_is_datamap().
* object maps, ie. set_is_objmap().

This patch adds helper functions to check for the map type.

set_is_map() allows you to check for either map type.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>