Use right function to set TLS1.3 restrictions in show-tls

Use right function to set TLS1.3 restrictions in show-tls

The last version of the patch used the TLS1.2 version
tls_ctx_restrict_ciphers to set the restrictions for both
TLS 1.3 and TLS1.2 instead of using tls_ctx_restrict_ciphers_tls13
for TLS1.3.

Also fix minor style problem while I am touching the function
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20181011220639.7316-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg17755.html

Signed-off-by: Gert Doering <gert@greenie.muc.de>