Clarify MTU in advanced Settings. (#3296)

* Update build.func

* Update build.func

Author: michelroegl-brunner

misc/build.func

@@ -715,7 +715,7 @@ advanced_settings() {
   fi
   echo -e "${DISABLEIPV6}${BOLD}${DGN}Disable IPv6: ${BGN}$DISABLEIP6${CL}"
 
-  if MTU1=$(whiptail --backtitle "Proxmox VE Helper Scripts" --inputbox "Set Interface MTU Size (leave blank for default [1500])" 8 58 --title "MTU SIZE" 3>&1 1>&2 2>&3); then
+  if MTU1=$(whiptail --backtitle "Proxmox VE Helper Scripts" --inputbox "Set Interface MTU Size (leave blank for default [The MTU of your selected vmbr, default is 1500])" 8 58 --title "MTU SIZE" 3>&1 1>&2 2>&3); then
     if [ -z $MTU1 ]; then
       MTU1="Default"
       MTU=""