Ensure links are protected

[cmhe]

Is your feature request related to a problem? Please describe.
Currently linux-baseline does not check if link protection is enabled.

Describe the solution you'd like
Create a additional check for those sysctls:

• fs.protected_fifos == 1 or 2
• fs.protected_hardlinks == 1
• fs.protected_regular == 2
• fs.protected_symlinks == 1

Additional context
Unprotected symlinks are a long-standing cause for security issues. See the official kernel docs about this.

Those settings should be default on most current Linux distributions, but it still makes sense to check those. Other security check projects like Lynis already checks those as well. See here