nginx: use geo module instead of $remote_addr regexp

nginx/selftest.conf

+geo $ssn {
+    default             false;
+
+    # StuSta
+    10.150.0.0/17       true;
+    141.84.69.0/24      true;
+    2001:4ca0:200::/48  true;
+
+    # MB67
+    10.149.8.0/21       true;
+    129.187.166.156/30  true;
+    2001:4ca0:201::/48  true;
+}
+
 server {
     listen 80;
     listen [::]:80;
@@ -18,10 +32,6 @@ server {
 
     location /status {
         default_type application/json;
-        set $ssn "true";
-        if ( $remote_addr !~ "^((10\.150\.[01]?\d?\d\..*)|(141\.84\.69\..*)|(10\.149\.0?([0-9]|1[0-5])\..*)|(129\.187\.166\.15[6-9])|(2001:4ca0:0?20[01]:.*)|(10\.0\..*))") {
-            set $ssn "false";
-        }
         return 200 "{\"ip\": \"$remote_addr\", \"ssn\": $ssn}\n";
     }