nettle: use the nettle_get_secp API when available
That utilizes the nettle_get_secp_*
accessor functions when available in nettle to stay compatible with the new API in 3.4.
Checklist
-
Code modified for feature
Reviewer's checklist:
-
Any issues marked for closing are addressed -
There is a test suite reasonably covering new functionality or modifications -
Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTION.md
-
This feature/change has adequate documentation added -
No obvious mistakes in the code