According to https://criu.org/API_compliance, the C-library
doesn't support the pageserver option.
This patch contains the functions
`criu_(local_)set_page_server_address_port()`
that allow to specify on which ip and tcp-port the pageserver
is listening.

This patch affects only the c-lib, as criu-rpc already supports the
pageserver settings.
Signed-off-by: Martin Wührer <martin.wuehrer@artech.at>
Signed-off-by: Andrei Vagin <avagin@gmail.com>