tst-process_madvise: Check process_madvise-syscall support.

So far this test checks if pidfd_open-syscall is supported,
which was introduced with linux 5.3.

The process_madvise-syscall was introduced with linux 5.10.
Thus you'll get FAILs if you are running a kernel in between.

This patch adds a check if the first process_madvise-syscall
returns ENOSYS and in this case will fail with UNSUPPORTED.
Reviewed-by: Florian Weimer <fweimer@redhat.com>