fix(linux): check for correct sign of netlink error code (#8087)

We've previously tried to handle the "No such process" error from
netlink when it tries to remove a route that no longer exists. What we
failed to do is use the correct sign for the error code as netlink
errors are always negative, yet when printed, the are positive numbers.

rust/bin-shared/src/tun_device_manager/linux.rs

@@ -287,7 +287,7 @@ async fn remove_route(route: &IpNetwork, idx: u32, handle: &Handle) {
 
     // "No such process" is another version of "route does not exist".
     // See <https://askubuntu.com/questions/1330333/what-causes-rtnetlink-answers-no-such-process-when-using-ifdown-command>.
-    if matches!(&err, NetlinkError(err) if err.raw_code() == ESRCH) {
+    if matches!(&err, NetlinkError(err) if err.raw_code() == -ESRCH) {
         return;
     }