i40e: Add and use helper to reconfigure TC for given VSI

Add helper i40e_vsi_reconfig_tc(vsi) that configures TC
for given VSI using previously stored TC bitmap.

Effectively replaces open-coded patterns:

enabled_tc = vsi->tc_config.enabled_tc;
vsi->tc_config.enabled_tc = 0;
i40e_vsi_config_tc(vsi, enabled_tc);

Reviewed-by: Michal Schmidt <mschmidt@redhat.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>