Enable TCP BBR

- Improve VPN performance by enabling the TCP BBR congestion control
  algorithm on supported systems (e.g. Ubuntu 18.04+, Debian 10+,
  CentOS 8+) during VPN setup.
  References:
  https://cloud.google.com/blog/products/networking/tcp-bbr-congestion-control-comes-to-gcp-your-internet-just-got-faster
  https://github.com/hwdsl2/setup-ipsec-vpn/blob/master/docs/bbr.md

vpnsetup_centos.sh

@@ -549,6 +549,12 @@ net.core.rmem_max = 12582912
 net.ipv4.tcp_rmem = 10240 87380 12582912
 net.ipv4.tcp_wmem = 10240 87380 12582912
 EOF
+    if modprobe -q tcp_bbr; then
+cat >> /etc/sysctl.conf <<'EOF'
+net.core.default_qdisc = fq
+net.ipv4.tcp_congestion_control = bbr
+EOF
+    fi
   fi
 }
 

vpnsetup_ubuntu.sh

@@ -499,6 +499,12 @@ net.core.rmem_max = 12582912
 net.ipv4.tcp_rmem = 10240 87380 12582912
 net.ipv4.tcp_wmem = 10240 87380 12582912
 EOF
+    if modprobe -q tcp_bbr; then
+cat >> /etc/sysctl.conf <<'EOF'
+net.core.default_qdisc = fq
+net.ipv4.tcp_congestion_control = bbr
+EOF
+    fi
   fi
 }