linux-cp: Add delegate to adjacencies

linux-cp: Add delegate to adjacencies

Type: improvement

When an adjacency is created, add the linux-cp delegate on the new
adjacency so we can later deal with modifications & deletions in our
cache of adjacency data.

Add a pool of hash keys and associate the pool index for a particular
key with the adj_delegate_t. If the rewrite on an adjacency is changed,
this will allow us to delete the old hash table entry and it will not
become orphaned.

Signed-off-by: Matthew Smith <mgsmith@netgate.com>
Change-Id: I072b960c02cf377d66f7d18b8c0e9e05824a0ca3