init.rc: increase readahead window multiplier for POSIX_FADV_SEQUENTIAL files

Set readahead window multiplier for POSIX_FADV_SEQUENTIAL files as 16 to
enhance file read performance like a language package loading.

Bug: 192011293
Test: adb shell cat /dev/sys/fs/by-name/userdata/seq_file_ra_mul
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Change-Id: I7f7e4339651be2d6aa99b07bcb12ab62136a940e
Merged-In: I7f7e4339651be2d6aa99b07bcb12ab62136a940e