filter_geoip2: allow nested lookup paths beyond depth 2

geoip2 filter limited lookup path splitting to depth 2, which caused
nested paths like 'subdivisions.0.names.en' to be truncated and fail
at runtime.

This change allows unlimited nesting by using flb_utils_split(..., 4),
making array-backed fields such as subdivisions accessible.

So, we need to accept subdivitions elements.

For example,
the following configuration could be broken on loading because of
containing three dots or more.

Signed-off-by: Hiroshi Hatake <hiroshi@chronosphere.io>

Author: cosmo0920

plugins/filter_geoip2/geoip2.c

@@ -240,7 +240,7 @@ static void add_geoip_fields(msgpack_object *map,
         pos = strstr(record->val, "}");
         memset(key, '\0', sizeof(key));
         strncpy(key, record->val + 2, pos - (record->val + 2));
-        split = flb_utils_split(key, '.', 2);
+        split = flb_utils_split(key, '.', 8);
         split_size = mk_list_size(split);
         path = flb_malloc(sizeof(char *) * (split_size + 1));
         i = 0;