i40e: Missing response checks in driver when starting/stopping FW LLDP

Driver updated pf->flags before calling i40e_aq_start_lldp().
This patch moved down updating pf->flags down so flags will be
updated only in case of successful i40e_aq_start_lldp() call.
Also was introduced is_reset_needed local flag to avoid unnecessary h/w
reset in case 40e_aq_start_lldp() didn't change lldp state.

Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>