Fix Libreswan flags

- Fix Libreswan flags on e.g. some Raspbian versions, where VERSION_CODENAME
  is undefined in /etc/os-release
  Ref: https://github.com/libreswan/libreswan/blob/main/mk/defaults/linux.mk

extras/vpnupgrade.sh

@@ -180,7 +180,7 @@ cat > Makefile.inc.local <<'EOF'
 WERROR_CFLAGS=-w
 USE_DNSSEC=false
 EOF
-if [ "$SWAN_VER" != "4.1" ] || [ "$debian_ver" = "8" ]; then
+if [ "$SWAN_VER" != "4.1" ] || [ "$debian_ver" = "8" ] || ! grep -qs 'VERSION_CODENAME=' /etc/os-release; then
 cat >> Makefile.inc.local <<'EOF'
 USE_DH31=false
 USE_NSS_AVA_COPY=true
@@ -190,7 +190,7 @@ EOF
 fi
 if [ "$SWAN_VER" = "3.31" ] || [ "$SWAN_VER" = "3.32" ] || [ "$SWAN_VER" = "4.1" ]; then
   echo "USE_DH2=true" >> Makefile.inc.local
-  if [ "$SWAN_VER" != "4.1" ] || [ "$debian_ver" = "8" ]; then
+  if [ "$SWAN_VER" != "4.1" ] || [ "$debian_ver" = "8" ] || ! grep -qs 'VERSION_CODENAME=' /etc/os-release; then
     if ! grep -qs IFLA_XFRM_LINK /usr/include/linux/if_link.h; then
       echo "USE_XFRM_INTERFACE_IFLA_HEADER=true" >> Makefile.inc.local
     fi

vpnsetup.sh

@@ -204,6 +204,17 @@ USE_DH2=true
 USE_NSS_KDF=false
 FINALNSSDIR=/etc/ipsec.d
 EOF
+if ! grep -qs 'VERSION_CODENAME=' /etc/os-release; then
+cat >> Makefile.inc.local <<'EOF'
+USE_DH31=false
+USE_NSS_AVA_COPY=true
+USE_NSS_IPSEC_PROFILE=false
+USE_GLIBC_KERN_FLIP_HEADERS=true
+EOF
+  if ! grep -qs IFLA_XFRM_LINK /usr/include/linux/if_link.h; then
+    echo "USE_XFRM_INTERFACE_IFLA_HEADER=true" >> Makefile.inc.local
+  fi
+fi
 if [ "$(packaging/utils/lswan_detect.sh init)" = "systemd" ]; then
   apt-get -yq install libsystemd-dev || exiterr2
 fi