ice: do Tx through PF netdev in slow-path

Tx can be done using PF netdev.

Checks before Tx are unnecessary. Checking if switchdev mode is set
seems too defensive (there is no PR netdev in legacy mode). If
corresponding VF is disabled or during reset, PR netdev also should be
down.

Reviewed-by: Marcin Szycik <marcin.szycik@linux.intel.com>
Signed-off-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Tested-by: Sujai Buvaneswaran <sujai.buvaneswaran@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>