openssl doesn't work on linux kernels before 4.11 (aka kernels without TCP_FASTOPEN_CONNECT)
If you build wget2 against openssl on a linux kernel before 4.11 it uses the pre-TCP_FASTOPEN_CONNECT
code path which isn't fully implemented in the openssl wrapper. Kernels starting with 4.11 work fine because the TCP_FASTOPEN_CONNECT
code path works. The workaround for pre-4.11 kernels is to use --no-tcp-fast-open
so that it doesn't try to use fast open at all.
For fast open to work with pre-4.11 kernels wget2's openssl wrapperr needs something like the sendmsg(MSG_FASTOPEN)
call like the gnutls wrapper has.