ip: functional interface to ip fragmentation

This provides a functional interface to IP fragmentation.
Allowing external features to fragment. Supports
arbitrary encap size, for e.g. MPLS or inner fragmentation
of tunnels.

This also removed dual loop in MAP that was fundamentally broken.

Type: fix
Signed-off-by: Ole Troan <ot@cisco.com>
Change-Id: Ia89ecec8ee3cbe2416edbe87630fdb714898c2a8
Signed-off-by: Ole Troan <ot@cisco.com>