docs: installation/upgrade/2.4-to-2.4.x - Document changed default for lmtp_user_concurrency_limit

Author: fleischie

docs/installation/upgrade/2.4-to-2.4.x.md

@@ -25,3 +25,4 @@ changed from `2.4.0` to `2.4.1`.
 | [[setting,mail_cache_fields]] | flags | flags hdr.date hdr.subject hdr.from hdr.sender hdr.reply-to hdr.to hdr.cc hdr.bcc hdr.in-reply-to hdr.message-id date.received size.virtual imap.bodystructure mime.parts hdr.references hdr.importance hdr.x-priority hdr.x-open-xchange-share-url pop3.uidl pop3.order |
 | `service/auth/unix_listener/auth-userdb/group` | (empty = root) | `$SET:default_internal_group` |
 | `service/lmtp/restart_request_count` | unlimited | 1 |
+| [[setting,lmtp_user_concurrency_limit]] | unlimited | 10 |