ipvs: Explictly clear ip_vs_stats members

In order to align the coding styles of ip_vs_zero_stats() and
its child-function ip_vs_zero_estimator(), clear ip_vs_stats
members explicitlty rather than doing a limited memset().

This was chosen over modifying ip_vs_zero_estimator() to use
memset() as it is more robust against changes in members
in the relevant structures. memset() would be prefered if
all members of the structure were to be cleared.

Cc: Sven Wegener <sven.wegener@stealer.net>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Sven Wegener <sven.wegener@stealer.net>