GHSA-vv6c-69r6-chg9: Go-Landlock in best-effort mode did not restrict TCP bind and connect operations correctly

When using the recommended “best-effort” mode, Go-Landlock did not restrict the TCP bind() and connect() operations any more when they were requested. This affects Go-Landlock users to whom both of the following conditions apply:

• They use Landlock rulesets that are supposed to restrict networking (through landlock.V4, landlock.V5, or self-configured).
• These Landlock rulesets are used in best-effort mode.

Typically, affected code uses the Go-Landlock API like this (the crucial part being the combination of V4/V5 and .BestEffort()):

err := landlock.V5.BestEffort().Restrict(...)

• This is a bug in the Go-Landlock library and does not affect programs that use Landlock via C or other language bindings.
• The bug only affects networking restrictions. File system restrictions continue to work as expected.