Fix Sysctl() in buffer size autodetection mode (#52824)

Fix Sysctl() in buffer size autodetection mode (#52824)

* Fix Sysctl() in buffer size autodetection mode

The code private static unsafe void Sysct() in the
Interop/BSD/System.Native/Interop.Sysctl.cs has two flaws in the case
value == null && len == 0.

First, in case of failure, this code doesn't call FreeHGlobal() on the memory it
allocated right before. I.e., we have pure memory leak.

Second, the "I don't know how much memory is needed, please allocated it by
yourself" idea standing behind value == null && len == 0 assumes the Sysctl()
itself being responsible to avoid ENOMEM condition. It could happen when, for
example, we ask to list all processes in the system: this list could be expanded
between first and second actual sysctl() calls, making the second call fail. So
instead of a single try, we should try to allocate a bit more memory and try
again; not force all our callers to do this themselves, by catching
InvalidOperationException and analyzing it.

Fixes #52823

* add missing IntPtr <-> int casts