Write boundary-mfp in kappa-*.hdf5 file

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (8bb93ee) 64.94% compared to head (d869785) 65.05%. Report is 1 commits behind head on develop.

Files	Patch %	Lines
phono3py/conductivity/utils.py	50.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #206 +/- ## =========================================== + Coverage 64.94% 65.05% +0.11% =========================================== Files 70 71 +1 Lines 12627 12671 +44 =========================================== + Hits 8200 8243 +43 - Misses 4427 4428 +1 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.