refactor: added error checking and various features

firewall/mullvad_tailscale.conf

@@ -0,0 +1,11 @@
+table inet mullvad_tailscale {
+  chain output {
+    type route hook output priority -100; policy accept;
+    ip daddr 100.64.0.0/10 ct mark set 0x00000f41 meta mark set 0x6d6f6c65;
+  }
+
+  chain input {
+    type filter hook input priority -100; policy accept;
+    ip saddr 100.64.0.0/10 ct mark set 0x00000f41 meta mark set 0x6d6f6c65;
+  }
+}