Add missing #ifdef SSL_OP_NO_TLSv1_1/2

Add missing #ifdef SSL_OP_NO_TLSv1_1/2

Release/2.4 supports older OpenSSL versions than master, so when
cherrypicking f8a92a4393a -> 2d705accea3e53 these code bits should
have received an #ifdef to ensure compatibility (as done for the
same define in other places in 2.4 already).  Add them now.

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Selva Nair <selva.nair@gmail.com>
Message-Id: <52e860ea74ac958309368374049f14bd.squirrel@webmail.bi.invoca.ch>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg16588.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>