subsys: fota_download: correcting URI check

[VTPeltoketo]

• HASH checksums are used to validate changed URI

[NordicBuilder]

Test specification

CI/Jenkins/NRF

• Integration Platforms

CI/Jenkins/integration

Test Module	File based changes	Manually selected	West overwrite
test-ci-nrfconnect-boot-fw-update	X
test-fw-nrfconnect-nrf-iot_mosh	X
test-fw-nrfconnect-nrf-iot_serial_lte_modem	X
test-fw-nrfconnect-nrf-iot_zephyr_lwm2m	X

Detailed information of selected test modules

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[NordicBuilder]

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[SeppoTakalo]

Looks functionally correct.

Please remove the extra Kconfig dependency and rename the variables to *_hash instead of *_sha256

[SeppoTakalo]

Squash both of these commits together. It is basically just one change.

[sigvartmh]

I assume this is either to speed up the check or to remove strcmp right? Anyways so far changes looks good to me.

[VTPeltoketo]

@sigvartmh There were two reasons: 1) There was a bug in the original code, the pointers of strcmp pointed to the same address. 2) strcmp requires a second buffer of URI and the buffer is quite big. We are running out of RAM and second buffer is not a viable solution.

[b-gent]

Suggested change

	* Verifies if download started with the same URI and resumes the interrupted download.
	* The library now verifies whether the download started with the same URI and resumes the interrupted download.

[VTPeltoketo]

Fixed