RDMA/rxe: Move the definitions for rxe_av.network_type to uAPI

RXE was wrongly using an internal kernel enum as part of its uAPI, split
this out into a dedicated uAPI enum just for RXE. It only uses the IPv4
and IPv6 values.

This was exposed by changing the internal kernel enum definition which
broke RXE.

Fixes: 1c15b4f2

 ("RDMA/core: Modify enum ib_gid_type and enum rdma_network_type")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>