send-email: Honour SMTP domain when using TLS

git-send-email sends two SMTP EHLOs when using TLS encryption, however
only the first, unencrypted EHLO uses the SMTP domain that can be
optionally specified by the user (--smtp-domain).  This is because the
call to hello() that produces the second, encrypted EHLO does not pass
the SMTP domain as an argument, and hence a default of
'localhost.localdomain' is used instead.

Fix by passing in the SMTP domain in this call.

Signed-off-by: Matthew Daley <mattjd@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>