net/mlx5e: kTLS, Cleanup redundant capability check

All callers of mlx5e_ktls_build_netdev() check capability
before the call.
Remove the repeated check in the function.

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Reviewed-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>