Refactor add_nat_rule into add_iptables_rule that is more general

weaver/weave

@@ -82,13 +82,20 @@ run_iptables() {
     iptables $IPTABLES_W "$@"
 }
 
-add_nat_rule() {
-    if ! run_iptables -t nat -C "$@" >/dev/null 2>&1
+# Add a rule to iptables, if it doesn't exist already
+add_iptables_rule() {
+    IPTABLES_TABLE="$1"
+    shift 1
+    if ! run_iptables -t $IPTABLES_TABLE -C "$@" >/dev/null 2>&1
     then
-        run_iptables -t nat -A "$@" >/dev/null
+        run_iptables -t $IPTABLES_TABLE -A "$@" >/dev/null
     fi
 }
 
+add_nat_rule() {
+    add_iptables_rule nat $@
+}
+
 setup_masquerading() {
     run_iptables -t nat -N WEAVE >/dev/null 2>&1 || true
     add_nat_rule POSTROUTING -j WEAVE