ANDROID: 16K: Fix swap header maxpages

On x86_64 device with emulated 16KiB page size, the calculation of the
swap space's max pages by the mkswap tool in userspace lead to a reduced
swap space size.

This is due to the fact that the userspace page size is 16KiB while the
kernel page size is still 4KiB.

If this is the case modify the maxpages to be in terms of 4KiB pages,
so that the entire swap file can be utilized.

Bug: 366098040
Test: Stress tested with aosp/3312673
Change-Id: I40646ec86b93deaa4839263900990aae3edc5196
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>