ONE-8: Fix adj signature issues

ONE-8: Fix adj signature issues

When inserting routes into ip4/6 fibs, we first added a dummy adjacency
and afterwards manually updated its rewrite header to enable src/dst
forwarding. The downside to this is that the adj signature is changed
and therefore when deleting a route the adjacency signature is not
removed from adj_index_by_signature hash resulting in crash if the same
adjacency is re-inserted.

This patch avoids the issue by enforcing the insertion of 'complete'
adjacencies thereby obviating the need to update the rewrite header.

Change-Id: Ib43bfe72a65e2cf9ef7685a99596eb1d7723e543
Signed-off-by: Florin Coras <[email protected]>