MAINTAINERS: add IPVS include files

Signed-off-by: Hannes Eder <heder@google.com>
Cc: Joe Perches <joe@perches.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>