Before this change, if --vfs-cache-mode writes or above was set and
--links was in use, when a symlink was saved then the VFS failed to
upload it. This meant when the VFS was restarted the link wasn't there
any more.
This was caused by the local backend, which we use to manage the VFS
cache, picking up the global --links flag.
This patch makes sure that the internal instantations of the local
backend in the VFS cache don't ever use the --links flag or the
--local-links flag even if specified on the command line.
Fixes#8367
b5e72e2fc3