OS400: Fix symbols

- s/CURLOPT_SOCKS_PROXY/CURLOPT_PRE_PROXY
  Follow-up to 7907a2be and 845522ca.

- Fix incorrect id for CURLOPT_PROXY_PINNEDPUBLICKEY.

- Add id for CURLOPT_ABSTRACT_UNIX_SOCKET.

Bug: https://github.com/curl/curl/issues/1237


Reported-by:  <jonrumsey@users.noreply.github.com>