Log Message:
mail/opensmtpd: update to 7.5.0p0

# Changes

* Added support for RFC 7505 "Null MX" handling and treat an MX of
  "localhost" as it were a "Null MX".
* Allow inline tables and filter listings in smtpd.conf(5) to span over
  multiple lines.
* Enabled DSN for the implicit socket too.
* Added the no-dsn option for listen on socket too.
* Reject headers that start with a space or a tab.
* Fixed parsing of the ORCPT parameter.
* Fixed table lookups of IPv6 addresses.
* Fixed handling of escape characters in To, From and Cc headers.
* Run LMTP deliveries as the recipient user again.
* Disallow custom commands and file reading in root's .forward file.
* Do not process other users .forward files when an alternate delivery
  user is provided in a dispatcher.
* Unify the table(5) parser used in smtpd(8) and makemap(8).
* Allow to use table(5) mappings on various match constraints.

 Portability fixes:

 * re-add ASR_IPV4_BEFORE_IPV6 compile-time knob to prefer connecting to
   IPv6 instead of IPv4.
 * update asr(3) and imsg with OpenBSD.
 * fixed rpath handling on NetBSD in the configure.