postfix: Update to 3.8.0

upstream changes:
-----------------
Postfix 3.7.8
  o Support to look up DNS SRV records in the Postfix SMTP/LMTP client, Based
    on code by Tomas Korbar (Red Hat). For example, with "use_srv_lookup =
    submission" and "relayhost = example.com:submission", the Postfix SMTP
    client will look up DNS SRV records for _submission._tcp.example.com, and
    will relay email through the hosts and ports that are specified with those
    records.
  o TLS obsolescence: Postfix now treats the "export" and "low" cipher grade
    settings as "medium". The "export" and "low" grades are no longer supported
    in OpenSSL 1.1.1, the minimum version required in Postfix 3.6.0 and later.
    Also, Postfix default settings now exclude deprecated or unused ciphers
    (SEED, IDEA, 3DES, RC2, RC4, RC5), digest (MD5), key exchange algorithms
    (DH, ECDH), and public key algorithm (DSS).
  o Attack resistance: the Postfix SMTP server can now aggregate
    smtpd_client_*_rate and smtpd_client_*_count statistics by network block
    instead of by IP address, to raise the bar against a memory exhaustion
    attack in the anvil(8) server; Postfix TLS support unconditionally disables
    TLS renegotiation in the middle of an SMTP connection, to avoid a CPU
    exhaustion attack.
  o The PostgreSQL client encoding is now configurable with the "encoding"
    Postfix configuration file attribute. The default is "UTF8". Previously the
    encoding was hard-coded as "LATIN1", which is not useful in the context of
    SMTP.
  o The postconf command now warns for #comment in or after a Postfix parameter
    value. Postfix programs do not support #comment after other text, and treat
    that as input.


(triaxx)