ipvs: Embed user stats structure into kernel stats structure

Instead of duplicating the fields, integrate a user stats structure into
the kernel stats structure. This is more robust when the members are
changed, because they are now automatically kept in sync.

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>
Reviewed-by: Julius Volz <juliusv@google.com>
Signed-off-by: Simon Horman <horms@verge.net.au>