net/mlx5: E-switch, Introduce flag to indicate if fdb table is created

Introduce flag to indicate if fdb table is created as a pre-step
to prepare for removing dependency between sriov and eswitch mode
in the downstream patches.

Signed-off-by: Chris Mi <cmi@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>