openvpn: updated to 2.5.5

Overview of changes in 2.5.5
============================

User-visible Changes
--------------------
- SWEET32/64bit cipher deprecation change was postponed to 2.7

- Windows: use network address for emulated DHCP server as default
  this enables use of a /30 subnet, which is needed when connecting
  to OpenVPN Cloud.

- require EC support in windows builds
  (this means it's no longer possible to build a Windows OpenVPN binary
  with an OpenSSL lib without EC support)

New features
------------
- Windows build: use CFG and Spectre mitigations on MSVC builds

- bring back OpenSSL config loading to Windows builds.
  OpenSSL config is loaded from %installdir%\SSL\openssl.cfg
  (typically: c:\program files\openvpn\SSL\openssl.cfg) if it exists.

  This is important for some hardware tokens which need special
  OpenSSL config for correct operation.

Bugfixes
--------
- Windows build: enable EKM

- Windows build: improve various vcpkg related build issues

- Windows build: fix regression related to non-writeable status files

- Windows build: fix regression that broke OpenSSL EC support

- Windows build: fix "product version" display (2.5..4 -> 2.5.4)

- Windows build: fix regression preventing use of PKCS12 files

- improve "make check" to notice if "openvpn --show-cipher" crashes

- improve argv unit tests

- ensure unit tests work with mbedTLS builds without BF-CBC ciphers

- include "--push-remove" in the output of "openvpn --help"

- fix error in iptables syntax in example firewall.sh script

- fix "resolvconf -p" invocation in example "up" script

- fix "common_name" environment for script calls when
  "--username-as-common-name" is in effect

Documentation
-------------
- move "push-peer-info" documentation from "server options" to "client"
  (where it belongs)

- correct "foreign_option_{n}" typo in manpage

- update IRC information in CONTRIBUTING.rst (libera.chat)

- README.down-root: fix plugin module name

(adam)