linux(4): Quiesce warning about madvise(..., -1)

This API misuse is intended to produce an error value to detect certain
bogus stub implementations of MADV_WIPEONFORK. We don't need to log a
warning about it.

Example:
https://boringssl.googlesource.com/boringssl/+/ad5582985cc6b89d0e7caf0d9cc7e301de61cf66%5E%21/

Reviewed by: emaste, trasz
Differential Revision: https://reviews.freebsd.org/D27017