net: Introduce ife encapsulation module

This module is responsible for the ife encapsulation protocol
encode/decode logics. That module can:
 - ife_encode: encode skb and reserve space for the ife meta header
 - ife_decode: decode skb and extract the meta header size
 - ife_tlv_meta_encode - encodes one tlv entry into the reserved ife
   header space.
 - ife_tlv_meta_decode - decodes one tlv entry from the packet
 - ife_tlv_meta_next - advance to the next tlv

Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Yotam Gigi <yotamg@mellanox.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Roman Mashak <mrv@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>