examples/l3fwd: add FIB infrastructure

examples/l3fwd: add FIB infrastructure

The purpose of this commit is to add the necessary function calls
and supporting infrastructure to allow the Forwarding Information Base
(FIB) library to be integrated into the l3fwd sample app.
Instead of adding an individual flag for FIB, a new flag '--lookup' has
been added that allows the user to select their desired lookup method.
The flags '-E' and '-L' have been retained for backwards compatibility.

Signed-off-by: Conor Walsh <conor.walsh@intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Vladimir Medvedkin <vladimir.medvedkin@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>