smtpsrv: Improve "Received" header standard compliance

Despite its loose appearance, the "Received" header has a reasonably
standarized format.

We were not following the standard format as closely as we should; this
rarely causes problems in this particular case, but there's no need to
deviate from it.

This patch changes the Received header generation as follows:

 - The "from" section now uses the remote address as canonical (for
   non-authenticated users) which provides more valuable information
   than the user-supplied EHLO address (which is also included).
 - The remote authenticated user is now hidden, for additional privacy.
 - Use the "with" optional clause.
 - Use the standard way of printing TLS cipher suite.
 - Use the standard way of printing address literals.

test/t-05-null_address/expected_dsr

@@ -20,10 +20,10 @@ Delivery to the following recipient(s) failed permanently:
 
 ----- Original message -----
 
-Received: from localhost (authenticated as user@testserver)
-	by testserver (chasquid)
+Received: from localhost
+	by testserver (chasquid) with ESMTPSA
+	tls *
 	(over *
-	(envelope from "user@testserver")
 	; *
 Date: *
 From: Mailer daemon <somewhere@horns.com>