The latest Openssl package for Openwrt is for Openssl 1.0.2h, as you can see here: github.com/openwrt-mirror/openwrt/tree/master/package/libs/openssl
OpenSSL 1.1.0 has a lot of changes compared to OpenSSL 1.0.2, so it isn't possible to just make a few changes to the Makefile in order to compile OpenSSL 1.1.0 for OpenWrt.
How can I cross-compile OpenSSL 1.1.0f for an OpenWRT router?