lib: add framework for allocating routing table identifier IDs

lib: add framework for allocating routing table identifier IDs

The library changes add 3 new messages to exchange between daemons and
ZEBRA.
- ZEBRA_TABLE_MANAGER_CONNECT,
- ZEBRA_GET_TABLE_CHUNK,
- ZEBRA_RELEASE_TABLE_CHUNK,
the need is that routing tables identifier are shared by various
services. For the current case, policy routing enhancements are planned
to be used in FRR. Poliy routing relies on routing tables identifiers
from kernels. It will be mainly used by the future policy based routing
daemon, but not only. In the flowspec case, the BGP will need also to
inject policy routing information into specific routing tables.
For that, the proposal is made to let zebra give the appropriate range
that is needed for all daemons.

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>