Fix compilation on Linux kernel >= 3.18.0

Since kernel commit 8a9522d2fe compilation fails as kvm_age_page
tracepoint had its signature changed, so update it accordingly.

Tested pointing to kernels:
    git reset --hard v3.17; make init/version.o
    git reset --hard v3.18-rc1; make init/version.o

Signed-off-by: André Goddard Rosa <andre.goddard@gmail.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>