Instead of returning IB_LINK_LAYER_ETHERNET from rxe_link_layer, return it
directly from get_link_layer callback and remove rxe_link_layer().

Fixes: 8700e3e7 ("Soft RoCE driver")
Link: https://lore.kernel.org/r/20200705104313.283034-5-kamalheib1@gmail.comSigned-off-by: Kamal Heib <kamalheib1@gmail.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>