IB/netlink: Add a new local service operation

This commits adds a new RDMA local service operation:
- IP to GID resolution.

The client request would include the ifindex of the outgoing interface
and would place in an attribute (LS_NLA_TYPE_IPV4 or LS_NLA_TYPE_IPV6)
the destnation IP.

The local service would answer with a message that has the attribute:
- LS_NLA_TYPE_DGID - The destination GID.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>