Documentation: git-send-email: correct statement about standard ports

Documentation: git-send-email: correct statement about standard ports

The current documentation states that servers typically listen on port
465 and calls this "ssmtp". While it's true that many mail servers use
port 465 for SSL smtp, this is non-standard, and hails from the days
before smtp and submission TLS support, that arrived in RFC2487 and
RFC3207. Port 465 is actually assigned by IANA for unrelated purposes,
and is mostly still used by mail servers today only to support Outlook
Express.

In any case, this patch helps the documentation better reflect both
standards and reality, while still helpfully mentioning ports numbers
that a user may wish to specify.

Signed-off-by: Wesley J. Landaker <wjl@icecavern.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>