IPSEC: SPD counters in the stats sgement

IPSEC: SPD counters in the stats sgement

- return the stats_index of each SPD in the create API call
- no ip_any in the API as this creates 2 SPD entries. client must add both v4 and v6 explicitly
- only one pool of SPD entries (rhter than one per-SPD) to support this
- no packets/bytes in the dump API. Polling the stats segment is much more efficient
  (if the SA lifetime is based on packet/bytes)
- emit the policy index in the packet trace and CLI commands.

Change-Id: I7eaf52c9d0495fa24450facf55229941279b8569
Signed-off-by: Neale Ranns <nranns@cisco.com>