ip_set: Fix compatibility with kernels between v3.3 and v4.5

ip_set: Fix compatibility with kernels between v3.3 and v4.5

These kernels does not have in their @struct netlink_dump_control method
that is used to prepare for netlink dump ->start(). This affects all
kernels that does not contain commit fc9e50f5a5a4 ("netlink: add a start
callback for starting a netlink dump").

Introduce fake value of HAVE_NETLINK_DUMP_START_ARGS equal to 7 that
never spot in the wild and set HAVE_NETLINK_DUMP_START_ARGS to 4 only
after explicit test if ->start() is available.

Fixes: 7725bf5ba041 ("netfilter: ipset: fix suspicious RCU usage in find_set_and_id")
Signed-off-by: Serhey Popovych <serhe.popovych@gmail.com>
Signed-off-by: Jozsef Kadlecsik <kadlec@netfilter.org>