Bring into line with libswiftnav dgnss state refactor

[henryhallam]

Untested!

It seems a little disingenuous to initalize the whole dgnss_state only on an as-needed basis when we gain > 4 sats. I'd be inclined to do that in solution_setup() instead. Thoughts?

/cc @fnoble @mookerji

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[mookerji]

I agree. I think the dgnss initialization should happen with a canonical setup.

[henryhallam]

retest this please

[fnoble]

lgtm (after HITL testing)

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[denniszollo]

retest this please

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[henryhallam]

Appears to cause hard faults on Piski 1227 in the test rack, but not on Piksi 1757 on my desk...