wolfssl: 3.13.0 -> 3.15.0

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/wolfssl/versions.

These checks were done:

- built on NixOS

- 0 of 0 passed binary check by having a zero exit code.
- 0 of 0 passed binary check by having the new version present in output.
- found 3.15.0 in filename of file in /nix/store/gx03mc7m4r07ybly7san7xk3v17pm264-wolfssl-3.15.0
- directory tree listing: https://gist.github.com/79fbf246bbacf1d8014bee57d274625a
- du listing: https://gist.github.com/1f19919b71d52208a236a55cf066a003