fix(build): skip empty gateway value in network config

When var_gateway is set to an empty string, the resulting gw= token
in the comma-separated network string causes pct create to fail with
a 'missing key in comma-separated list property' error.

Closes #13421

ct/graylog.sh

@@ -64,12 +64,6 @@ function update_script() {
 }
 
 start
-
-if [[ $(sysctl -n vm.max_map_count 2>/dev/null) -lt 262144 ]]; then
-  sysctl -w vm.max_map_count=262144 >/dev/null 2>&1
-  echo "vm.max_map_count=262144" >/etc/sysctl.d/graylog.conf
-fi
-
 build_container
 description
 

misc/build.func

@@ -3530,6 +3530,7 @@ build_container() {
   # Gateway
   if [[ -n "$GATE" ]]; then
     case "$GATE" in
+    ,gw=) ;;
     ,gw=*) NET_STRING+="$GATE" ;;
     *) NET_STRING+=",gw=$GATE" ;;
     esac