ipvs: allow rs_table to contain different real server types

Before now rs_table was used only for NAT real servers.
Change it to allow TUN real severs from different types,
possibly hashed with different port key.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>