This fixes a linkage error about `ossl_ssl_type` on platforms which do
not have socket, like WASI.

Even before this patch, some items are disabled under `OPENSSL_NO_SOCK` since
https://github.com/ruby/ruby/commit/ee22fad45d394818690c4a7586d7bb576ba67c56
However, due to some new use of OpenSSL::SSL::Socket over the past few years,
the build under `OPENSSL_NO_SOCK` had been broken.

This patch guards whole `OpenSSL::SSL` items by `OPENSSL_NO_SOCK`.

[ky: adjusted to apply on top of my previous commit that removed the
OpenSSL::ExtConfig, and added a guard to lib/openssl/ssl.rb.]

https://github.com/ruby/openssl/commit/b0cfac6a96