[IPV6]: Add ORCHID prefix to address label table

Add a new label for Overlay Routable Cryptographic Hash Identifiers
(RFC 4843) prefix 2001:10::/28 to help proper source address
selection.

ORCHID addresses are used by for example Host Identity Protocol. They are 
global and routable, but they currently need support from both endpoints 
and therefore mixing regular and ORCHID addresses for source and 
destination is a bad idea in general case.

Signed-off-by: Juha-Matti Tapio <jmtapio@verkkotelakka.net>
Signed-off-by: David S. Miller <davem@davemloft.net>