cni: Use sysctl library
cni: Use sysctl library

Instead of writing to sysctl files manually, this change makes use of
the sysctl library introduced in 759ae501d9df.

Signed-off-by: Michal Rostecki <82ebf970c69340aebb770c3853be5fd96a3eb584@opensuse.org>

tklauser/cilium,tgraf/cilium,michi-covalent/cilium,tklauser/cilium,tklauser/cilium,michi-covalent/cilium,cilium-team/cilium,tgraf/cilium,cilium/cilium,cilium/cilium,cilium/cilium,tgraf/cilium,cilium-team/cilium,tklauser/cilium,cilium/cilium,tgraf/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium