source bastille_network_pf_ext_if from bastille config when loading rdr rule

usr/local/share/bastille/rdr.sh

@@ -159,7 +159,7 @@ load_rdr_rule() {
 
     local inet="${1}"
     local if_name="${2}"
-    local if=ext_if=\"${2}\"
+    local if="${bastille_network_pf_ext_if}"=\"${2}\"
     local src="${3}"
     local dst="${4}"
     local proto="${5}"
@@ -414,4 +414,4 @@ while [ "$#" -gt 0 ]; do
             fi
             ;;
     esac
-done
+done