libipvs: allow IPv4 RS in IPv6 VS and vice versa

This change syncronizes local copy of libipvs with the upstream (kernel/ipvsadm/ipvsadm.git) to the date.
IPVS in Linux 3.18 will include the feature of mixing of tunneled RS families in single VS by Alex Gartrell.

The compatibility with older kernel versions is kept.
libipvs: minor bugfix with retreiving dest af

This change needs to be sent to the ipvsadm upstream, too.
This clarifies the previous commit, so there is no need to mention it in the changelog.
ipvs, bug: quorum state was flapping when Q < H

When a service had quorum < hysteresis, the lower threshold of RS weights was calculated incorrecly.

Unsigned arythmetics was used, so errors like this appeared in log:
  Keepalived_healthcheckers[2535]: Lost quorum 1-2=18446744073709551615 > 10 for VS

The up -> down quorum state transition was happening every time when alive RS set was changed.

This bug was in place since keepalived-1.2.9
Merge pull request #112 from andriyanov/ya_build_3

libipvs extensions. IPVS quorum bugfixes.