Tidy up /etc/sysctl.conf and add WAN tuning to outward facing machines

[kreczko]

Conflicting entries

There currently exist conflicting entries in the sysctl.conf, e.g.

Controls IP packet forwarding

net.ipv4.ip_forward = 0
......

Recomended for pxe/libvirt

net.ipv4.ip_forward = 1

WAN Tuning

net.ipv4.tcp_rmem = 4096 131072 8288608
net.ipv4.tcp_wmem = 4096 131072 8388608
net.core.netdev_max_backlog = 3000
net.core.rmem_default = 131072
net.core.wmem_default = 131072
net.core.rmem_max = 8388608
net.core.wmem_max = 8388608
net.ipv4.tcp_congestion_control = htcp