lib, rip, ripng, eigrp: rework if_rmap context

lib, rip, ripng, eigrp: rework if_rmap context

so as to handle ri/ripng/eigrp multiple instances, the need is to
encapsulate if_rmap hash table into a container context self to each
instance. This work then reviews the if_rmap api, mainly by adding a
if_rmap_ctx context, that is passed for each exchange between library
and the daemon.

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