RDMA/mlx5: Block FDB rules when not in switchdev mode

RDMA/mlx5: Block FDB rules when not in switchdev mode

BugLink: https://bugs.launchpad.net/bugs/1934012
commit edc0b0bccc9c80d9a44d3002dcca94984b25e7cf upstream.

Allow creating FDB steering rules only when in switchdev mode.

The only software model where a userspace application can manipulate
FDB entries is when it manages the eswitch. This is only possible in
switchdev mode where we expose a single RDMA device with representors
for all the vports that are connected to the eswitch.

Fixes: 52438be44112 ("RDMA/mlx5: Allow inserting a steering rule to the FDB")
Link: https://lore.kernel.org/r/e928ae7c58d07f104716a2a8d730963d1bd01204.1623052923.git.leonro@nvidia.com
Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>