Increase REXML expansion text limit

MSP-9532

* Increase to reasonable size to handle larger xml file expansion on import
* Prevents the 'RuntimeError entity expansion has grown too large' error that prevents import

Author: ccatalan-r7

lib/msf/core/db_manager/import.rb

@@ -129,6 +129,8 @@ def import_file(args={}, &block)
       end
     end
 
+    # Override REXML's expansion text limit to 50k (default: 10240 bytes)
+    REXML::Security.entity_expansion_text_limit = 51200
 
     if block
       import(args.merge(:data => data)) { |type,data| yield type,data }