sysctl: improve KASLR effectiveness for mmap

sysctl: improve KASLR effectiveness for mmap

By feeding more random bits into mmap allocation, the
effectiveness of KASLR will be improved, making attacks
trying to bypass address randomisation more difficult.

Changed sysctl values are:

vm.mmap_rnd_bits = 32 (default: 28)
vm.mmap_rnd_compat_bits = 16 (default: 8)

This patch backports the same change made in IPFire 2.x into
IPFire 3.x .

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>