lrdp_v2 : Fix vmalloc pages accounting

The root cause is because we were using vm_struct->size to account vmalloc
pages. While for no VM_NO_GUARD set, linux will add one more page_size in,
That'll increase total size. I’m using vm_struct->nr_pages instead now.
In the same time, Using nr_vmalloc_pages to account vmalloc pages if it's
there.

Change-Id: I74d492e2577d280717758c367367dd9b6d82db2c
Signed-off-by: Zhenhua Huang <zhenhuah@codeaurora.org>