docs: Data Upload

[ntlhui]

• src/cellular/dataUpload.hpp:49: error: Member exitState(void) (function) of class DataUpload is not documented.
• src/cellular/dataUpload.hpp:50: error: Member can_upload(void) (function) of class DataUpload is not documented.
• src/cellular/dataUpload.hpp:47: error: Member initSuccess (variable) of class DataUpload is not documented.
• src/cellular/dataUpload.hpp:48: error: Member lastConnectTime (variable) of class DataUpload is not documented.
• <can_upload>:1: error: parameters of member DataUpload::can_upload are not documented
• :1: error: parameters of member DataUpload::exitState are not documented

ed2263e

[Tylody]

Seems like DataUpload lastConnectTime (type of system_tick_t) has no uses outside of dataUpload.hpp. Should I remove it?

[ntlhui]

Seems like DataUpload lastConnectTime (type of system_tick_t) has no uses outside of dataUpload.hpp. Should I remove it?

lastConnectTime is likely a remnant or incomplete implementation of rate limiting calls to Particle.connect - previously, we could not do more than 1 call per second to Particle.connect. Leave this in place for now, we need to investigate whether the rate limiting is still a concern.