echo "deb http://old-releases.ubuntu.com/ubuntu yakkety main" > /etc/apt/sources.list.d/yakkety.list
apt-get update
apt-get install -y ssh
rm /etc/apt/sources.list.d/yakkety.list
apt-get update

ssh -V
OpenSSH_7.3p1 Ubuntu-1, OpenSSL 1.0.2g  1 Mar 2016

mkdir ~/.ssh/config.d
sed -i '1iInclude config.d/*' ~/.ssh/config

Links
https://superuser.com/questions/247564/is-there-a-way-for-one-ssh-config-file-to-include-another-one