[IPVS]: Add sysctl documentation

* Derived from http://www.linuxvirtualserver.org/docs/sysctl.html, v1.4
  maintained by Wensong Zhang

* Adjusted preample to match ip-sysctl.txt

* Sorted options into alphabetical order

* Added expire_quiescent_template

* Removed timeout_* which are no longer present

* Incoporated doc/debug-levels.txt from IPVS source tree into
  description of ipvs_debug

* Minor spelling fixes

* Further editing more than welcome

Signed-Off-By: Horms <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>