fib: add FIB library

fib: add FIB library

Add FIB (Forwarding Information Base) library. This library
implements a dataplane structures and algorithms designed for
fast longest prefix match.
Internally it consists of two parts - RIB (control plane ops) and
implementation for the dataplane tasks.
Initial version provides two implementations for both IPv4 and IPv6:
dummy (uses RIB as a dataplane) and DIR24_8 (same as current LPM)
Due to proposed design it allows to extend FIB with new algorithms
in future (for example DXR, poptrie, etc).

Signed-off-by: Vladimir Medvedkin <vladimir.medvedkin@intel.com>