[IPVS]: Use msleep_interruptable() instead of ssleep() aka msleep()

Dean Manners notices that when an IPVS synchonisation daemons are
started the system load slowly climbs up to 1. This seems to be related
to the call to ssleep(1) (aka msleep(1000) in the main loop. Replacing
this with a call to msleep_interruptable() seems to make the problem go
away. Though I'm not sure that it is correct.

This is the second edition of this patch, which replaces ssleep()
in the main loop for both the master and backup threads, as well
as some thread synchronisation code. The latter is just for thorougness
as it shouldn't be causing any problems.

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