Add adjustStartupTimeout() functionality

[adamgarbo]

Hi @PaulZC,

A small PR to add functionality to control the startup timeout of the Iridium modem. This is perhaps more relevant to users of the RockBLOCK, who are required to wait for the default duration of 240 seconds if their modem is not starting up properly.

The startup timeout continues to default to the original period of 240 seconds as specified by:

#define ISBD_STARTUP_MAX_TIME           240

Similar to the other timeout functions, this value can now be modified using: modem.adjustStartupTimeout(60);

A quick test shows the timeout working as intended:

10:01:34.945 -> Starting modem...
10:02:35.541 -> Begin failed: error 5
10:02:35.541 -> No modem detected: check wiring.

Cheers,
Adam

[PaulZC]

Looks good @adamgarbo - thank you!
Merging...
I'll release it after a quick test.
Paul