Add min size for smtp_listen strings

  Variant[Array[String], String]  $root_mail_recipient = 'nobody',      # root_mail_recipient

  Optional[Boolean]               $chroot              = undef,

  Boolean                         $satellite           = false,

  Variant[Array[String], String]  $smtp_listen         = '127.0.0.1',   # postfix_smtp_listen

  Variant[Array[String[1]], String[1]] $smtp_listen    = '127.0.0.1',   # postfix_smtp_listen

  Boolean                         $use_amavisd         = false,         # postfix_use_amavisd

  Boolean                         $use_dovecot_lda     = false,         # postfix_use_dovecot_lda

  Variant[Integer[2, 3], Boolean] $use_schleuder       = false,         # postfix_use_schleuder