RDMA/rxe: Fix small problem in network_type patch

RDMA/rxe: Fix small problem in network_type patch

The patch referenced below has a typo that results in using the wrong L2
header size for outbound traffic. (V4 <-> V6).

It also breaks kernel-side RC traffic because they use AVs that use
RDMA_NETWORK_XXX enums instead of RXE_NETWORK_TYPE_XXX enums. Fix this by
transcoding between these enum types.

Fixes: e0d696d201dd ("RDMA/rxe: Move the definitions for rxe_av.network_type to uAPI")
Link: https://lore.kernel.org/r/20201016211343.22906-1-rpearson@hpe.com
Signed-off-by: Bob Pearson <rpearson@hpe.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>