net/mlx5e: Modify slow path rules to go to slow fdb

While extending available range of supported chains/prios referenced commit
also modified slow path rules to go to FT chain instead of actual slow FDB.
However neither of existing users of the MLX5_ATTR_FLAG_SLOW_PATH
flag (tunnel encap entries with invalid encap and flows with trap action)
need to match on FT chain. After bridge offload was implemented packets of
such flows can also be matched by bridge priority tables which is
undesirable. Restore slow path flows implementation to redirect packets to
slow_fdb.

Fixes: 278d51f2 ("net/mlx5: E-Switch, Increase number of chains and priorities")
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Paul Blakey <paulb@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>