help: Disable PPTP connection tracking

create: cli-shell-api exists system conntrack modules gre disable
        if [ $? == 0 ]; then
          # Do nothing, this case is handled in GRE module templates
          :;
        else
          sudo rmmod nf_nat_pptp
          sudo rmmod nf_conntrack_pptp
        fi

# PPTP shouldn't be enabled when GRE is disabled because PPTP depends on it
delete: cli-shell-api exists system conntrack modules gre disable
        if [ $? == 0 ]; then
          echo "Error: can not enable PPTP connection tracking when GRE connection tracking is disabled!"
          exit 1
        else
          sudo modprobe nf_conntrack_pptp
          sudo modprobe nf_nat_pptp
        fi