VXLAN multicast dst (remote) address support

VXLAN multicast dst (remote) address support

Added support for multicast vxlan tunnels which are used for bridge domain flooding instead
of flooding the all unicast tunnels in the bridge domain.

features added:
* conditional flooding to some of the BD members - based on existance of multicast tunnel member
* added local multicast adjacency - multicast packets are handled as the same as unicast - based on src (unicast) address
* refactored some of vxlan tunnel creation code - to unify ip4/6 handling

Change-Id: I60cca4124265a8dd4f6b2d6ea8701e52e7c1baa4
Signed-off-by: Eyal Bari <ebari@cisco.com>