ipvs: Added plugin to collect IPVS connection statistics.

ipvs: Added plugin to collect IPVS connection statistics.

This plugin collects detailed statistics for each IPVS service and it's
destinations. It is based on ipvsadm and libipvs by Wensong Zhang and
Peter Kese. The plugin requires a Linux (>= 2.6) kernel.

See http://www.linuxvirtualserver.org/software/index.html for more details
about IPVS.

A new DS type "connections" (value:COUNTER:0:U) has been added to
types.db.

Signed-off-by: Sebastian Harl <sh@tokkee.org>
Signed-off-by: Florian Forster <octo@huhu.verplant.org>