SLB: ability to translate RS' address family

There are cases when you are using NAT LVS method and generate the
internal RS address based on the real one. Then you probably want
to store the original(real) RS address in DB. There is already the
way to translate the value os RSIP macro in local plugin.
But sometimes you want to translate IPv6 address into IPv4: virtual
service has IPv4 family, but the RS lacks of IPv4 global-scope address.
This patch allows you to do so.

generateConfig: compare expanded(translated) RS address length to VIP
length, not the original one