Adding Tomato ifdef for netfilter chain to check
Created by: edrikk
To allow for "drop-in" upgrades of Miniupnp within Tomato firmware, submitting this change back upstream. Original source: https://bitbucket.org/kille72/tomato-arm-kille72/commits/b9d9e4b0ed761c6cdddd1227676b08bce2934481?at=shibby-arm
Have used ifdef for clarity of why the "new" entry is there (i.e. Tomato)