Enable setting and removing fixed position via remote admin

[djholt]

Based on recent firmware change to allow remote admin position config.

Question: do we need to handle old firmware versions with this change?

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 8 lines in your changes missing coverage. Please review.

Project coverage is 60.91%. Comparing base (48a06c6) to head (40353a3).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
meshtastic/node.py	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #675      +/-   ##
==========================================
- Coverage   60.94%   60.91%   -0.04%     
==========================================
  Files          24       24              
  Lines        3690     3689       -1     
==========================================
- Hits         2249     2247       -2     
- Misses       1441     1442       +1     

Flag	Coverage Δ
unittests	60.91% <33.33%> (-0.04%)	⬇️

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[ianmcorvidae]

Looks good! Thanks for picking this up, I hadn't gotten to it yet. I don't think we need to worry about older firmware versions. They'll reject any updates that get sent by this, but if someone hasn't updated they're probably aware of that constraint anyway.