fix #840: enable device time request by default

[dhineshkumarmcci]

No description provided.

[terrillmoore]

Hi, can you add a note to README.md, and also please change the version in lmic.h to something like 4.2.0-pre1? Thanks!

[terrillmoore]

One other thing -- please use git rebase -i and change the commit log message to be something like "Fix #840: Enable device time request by default" (it already was "enabled" in some sense, what you're changing is the default, so it will clarify to change the commit log, for tracking). (I change PR #844's title, but changing the commit log requires a git rebase -i to edit the commit log. Then you'll need to do a git push -f to issue840.)

[terrillmoore]

Please do a search for LMIC_ENABLE_DeviceTimeReq.

• It is used in ci/platformio.sh; we should remove it (now that it's the default).
• We should add a test to confirm that LMIC_ENABLE_DeviceTimeReq=0 still compiles correctly.
• We need to document the default state (README.md line 345). We should state "Prior to v4.2.0-pre1, the default was that device network-time requests were disabled. As of v4.2.0-pre1, the default is that device network-time requests are enabled."

[dhineshkumarmcci]

* We should add a test to confirm that `LMIC_ENABLE_DeviceTimeReq=0` still compiles correctly.

Added tests with disabling device-time request, using ttn-otaa.ino for regions US and EU.

arduino-lmic/ci/platformio.sh

Lines 65 to 67 in 7c73957

	# Compile "ttn-otaa" example in US and EU with Device-time request disabled
	PLATFORMIO_BUILD_FLAGS='-D CFG_us915 -D CFG_sx1276_radio -D LMIC_ENABLE_DeviceTimeReq=0 -D COMPILE_REGRESSION_TEST -D ARDUINO_LMIC_PROJECT_CONFIG_H_SUPPRESS' platformio ci --lib . --board heltec_wifi_lora_32 'examples/ttn-otaa/ttn-otaa.ino'
	PLATFORMIO_BUILD_FLAGS='-D CFG_eu868 -D CFG_sx1276_radio -D LMIC_ENABLE_DeviceTimeReq=0 -D COMPILE_REGRESSION_TEST -D ARDUINO_LMIC_PROJECT_CONFIG_H_SUPPRESS' platformio ci --lib . --board heltec_wifi_lora_32 'examples/ttn-otaa/ttn-otaa.ino'