ice: Don't tx before switchdev is fully configured

There is possibility that ice_eswitch_port_start_xmit might be
called while some resources are still not allocated which might
cause NULL pointer dereference. Fix this by checking if switchdev
configuration was finished.

Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Wojciech Drewek <wojciech.drewek@intel.com>
Tested-by: Sujai Buvaneswaran <sujai.buvaneswaran@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>