As most of the `criu_(local_)*` functions already call `strdup()`,
it is possible, to change the function signature to `const char *`.

As the struct `criu_opts` already contains a `const char *
service_binary`, also the member `service_address` is changed to
`const char`.

Additonally, also the function `criu_local_set_freeze_cgroup()` now
calls `strdup()`.
Signed-off-by: Martin Wührer <martin.wuehrer@artech.at>
Signed-off-by: Andrei Vagin <avagin@gmail.com>