Update to OpenSMTPD 5.3.1p1

Features:
=========

  * add support for local deliveries through LMTP
    contributed by Ashish SHUKLA


BugFixes:
=========

  * accept clients that use the [IPv6:...] notation in their EHLO
  * do not replace '/' with ':' in %{user.directory} expansion
  * fix possible crash upon reload in table_db API
  * do not close session on temporary failure of a recipient
  * sync asr with latest bugfixes from OpenBSD
  * various minor fixes