Sync LuCI and unbound.sh ttl-min limitations / remove or increase them

@EricLuehrsen

The max allowed value in /usr/lib/unbound/unbound.sh is 1800

  if [ $UB_TTL_MIN -gt 1800 ] ; then
    logger -t unbound -s "ttl_min could have had awful side effects, using 300"
    UB_TTL_MIN=300
  fi

The max allowed value in /usr/lib/lua/luci/model/cbi/unbound/configure.lua is 1200

    tlm = s1:taboption("resource", Value, "ttl_min",
        translate("TTL Minimum"),
        translate("Prevent excessively short cache periods"))
    tlm.datatype = "and(uinteger,min(0),max(1200))"
    tlm.placeholder = "120"

I believe these two values should be the same.

While we’re here, would you be open to removing this downstream restriction and maybe replacing it with a warning? If not, would you consider increasing the acceptable limit to 3600?

Choose one amd submit a pull request?