route/link: avoid dangling pointer in rtnl_link_set_slave_type()
route/link: avoid dangling pointer in rtnl_link_set_slave_type()

- don't leave a dangling pointer, in case we unset the
  kind.

- try first to clone the string. If that fails, return early
  without modifying the link. Only start modifying the link,
  after we know it's going to succeed.

thom311/libnl,thom311/libnl,thom311/libnl,greearb/libnl-ct,greearb/libnl-ct,greearb/libnl-ct