Use cache in map register message.

Use cache in map register message.

Map register messages are stored to special cache (hash map).

Key for this has map consists of eid-prefix, site-id and xtr-id.
Components of key are stored as byte arrays.

Value part of cache entry contains transformed value from key
(site-id and xtr-id and complete list of eid-prefixes). Additionaly
there is also timestamp (time of creation or refresh the cache entry),
want-map-notify value and complete original value of received map
register message.

Also new type of message mapping-keep-alive is added. This
notification is raised if map-register message is received and is
found in cache.

At the end if map-notify-bit is set then also notify message is
directly generated from southbound.

Change-Id: I6c5ba8e6ff226d5f4a7b5964159dc138a4bbfc33
Signed-off-by: Jozef Gloncak <jgloncak@cisco.com>