net/smtp: Add SNI support
It looks like SNI support has already been added to FTP, HTTP, IMAP, and POP. I think that SMTP is the only
Net::Protocol class remaining.
Since it's used by all of the
Net::Protocol classes, does it make more sense to move this into
Net::Protocol#ssl_socket_connect(socket, open_timeout, hostname) similar to the suggestion here: https://bugs.ruby-lang.org/issues/15594#change-77564 ?
See also the github PR: https://github.com/ruby/ruby/pull/2883