c-lib: strdup for service_address and service_binary

The functions criu_(local_)set_service_address and
criu_(local_)set_service_binary are the only functions that
do not create a copy of the given string arguments.
This may lead to problems, if the original string gets freed
but criu relies on them.

Additionally, the function criu_local_init_opts() assigns the
default service_binary now to opt->service_binary instead of
opt->service_address which is in my opinion the preferred way
since both are types of an anonymous union.

Signed-off-by: Martin Wührer <martin.wuehrer@artech.at>