pidref: do not tamper with pidref_acquire_pidfd_id() retval

If a pidfd id is passed to us, it must have originated from
somewhere, i.e. pidfs should be supported on the system.
Hence let's be honest about -EOPNOTSUPP, which might indicate
some bigger problems under the hood, rather than allowing
it to be turned into mild -ESRCH.

src/basic/pidref.c

@@ -137,7 +137,7 @@ int pidref_set_pid_and_pidfd_id(
 
         if (pidfd_id > 0) {
                 r = pidref_acquire_pidfd_id(&n);
-                if (r < 0 && !ERRNO_IS_NEG_NOT_SUPPORTED(r))
+                if (r < 0)
                         return r;
 
                 if (n.fd_id != pidfd_id)