Add support for swap-in request with multiple pages in Linux kernel 4.x

[juncgu]

In Linux kernel 4.x, swap-in (read) request is allowed to batch multiple pages. Multiple pages can be in a single swap-in request.
Infiniswap was initially developed on kernel 3.13 which only allows single page in a swap-in request. Therefore, current Infiniswap can only accept the swap-in request with one page. The multi-page swap-in request should be supported for kernel 4.x.

[leeymcj]

I think I solved this. I will share the code for revision.