In this case you have to Override the Onchange product_id definition(Function)   or Best solution is inherit onchange definition

@api.onchange('product_id')

def _onchange_product_id(self):

   result = super(account_invoice_line, self)._onchange_product_id()

   self.name = self.product_id.description

    return result

here  super(account_invoice_line, self) , account_invoice_line is the class name